diff -r 000000000000 -r 6474c204b198 browser/components/sessionstore/src/SessionStore.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/sessionstore/src/SessionStore.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,3687 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = ["SessionStore"];
+
+const Cu = Components.utils;
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const Cr = Components.results;
+
+const STATE_STOPPED = 0;
+const STATE_RUNNING = 1;
+const STATE_QUITTING = -1;
+
+const TAB_STATE_NEEDS_RESTORE = 1;
+const TAB_STATE_RESTORING = 2;
+
+const NOTIFY_WINDOWS_RESTORED = "sessionstore-windows-restored";
+const NOTIFY_BROWSER_STATE_RESTORED = "sessionstore-browser-state-restored";
+const NOTIFY_LAST_SESSION_CLEARED = "sessionstore-last-session-cleared";
+
+const NOTIFY_TAB_RESTORED = "sessionstore-debug-tab-restored"; // WARNING: debug-only
+
+// Maximum number of tabs to restore simultaneously. Previously controlled by
+// the browser.sessionstore.max_concurrent_tabs pref.
+const MAX_CONCURRENT_TAB_RESTORES = 3;
+
+// global notifications observed
+const OBSERVING = [
+  "domwindowopened", "domwindowclosed",
+  "quit-application-requested", "quit-application-granted",
+  "browser-lastwindow-close-granted",
+  "quit-application", "browser:purge-session-history",
+  "browser:purge-domain-data",
+  "gather-telemetry",
+];
+
+// XUL Window properties to (re)store
+// Restored in restoreDimensions()
+const WINDOW_ATTRIBUTES = ["width", "height", "screenX", "screenY", "sizemode"];
+
+// Hideable window features to (re)store
+// Restored in restoreWindowFeatures()
+const WINDOW_HIDEABLE_FEATURES = [
+  "menubar", "toolbar", "locationbar", "personalbar", "statusbar", "scrollbars"
+];
+
+const MESSAGES = [
+  // The content script gives us a reference to an object that performs
+  // synchronous collection of session data.
+  "SessionStore:setupSyncHandler",
+
+  // The content script sends us data that has been invalidated and needs to
+  // be saved to disk.
+  "SessionStore:update",
+
+  // The restoreHistory code has run. This is a good time to run SSTabRestoring.
+  "SessionStore:restoreHistoryComplete",
+
+  // The load for the restoring tab has begun. We update the URL bar at this
+  // time; if we did it before, the load would overwrite it.
+  "SessionStore:restoreTabContentStarted",
+
+  // All network loads for a restoring tab are done, so we should consider
+  // restoring another tab in the queue.
+  "SessionStore:restoreTabContentComplete",
+
+  // The document has been restored, so the restore is done. We trigger
+  // SSTabRestored at this time.
+  "SessionStore:restoreDocumentComplete",
+
+  // A tab that is being restored was reloaded. We call restoreTabContent to
+  // finish restoring it right away.
+  "SessionStore:reloadPendingTab",
+];
+
+// These are tab events that we listen to.
+const TAB_EVENTS = [
+  "TabOpen", "TabClose", "TabSelect", "TabShow", "TabHide", "TabPinned",
+  "TabUnpinned"
+];
+
+// The number of milliseconds in a day
+const MS_PER_DAY = 1000.0 * 60.0 * 60.0 * 24.0;
+
+Cu.import("resource://gre/modules/Services.jsm", this);
+Cu.import("resource://gre/modules/XPCOMUtils.jsm", this);
+Cu.import("resource://gre/modules/TelemetryTimestamps.jsm", this);
+Cu.import("resource://gre/modules/TelemetryStopwatch.jsm", this);
+Cu.import("resource://gre/modules/osfile.jsm", this);
+Cu.import("resource://gre/modules/PrivateBrowsingUtils.jsm", this);
+Cu.import("resource://gre/modules/Promise.jsm", this);
+Cu.import("resource://gre/modules/Task.jsm", this);
+
+XPCOMUtils.defineLazyServiceGetter(this, "gSessionStartup",
+  "@mozilla.org/browser/sessionstartup;1", "nsISessionStartup");
+XPCOMUtils.defineLazyServiceGetter(this, "gScreenManager",
+  "@mozilla.org/gfx/screenmanager;1", "nsIScreenManager");
+XPCOMUtils.defineLazyServiceGetter(this, "Telemetry",
+  "@mozilla.org/base/telemetry;1", "nsITelemetry");
+
+XPCOMUtils.defineLazyModuleGetter(this, "console",
+  "resource://gre/modules/devtools/Console.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "RecentWindow",
+  "resource:///modules/RecentWindow.jsm");
+
+XPCOMUtils.defineLazyModuleGetter(this, "GlobalState",
+  "resource:///modules/sessionstore/GlobalState.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PrivacyFilter",
+  "resource:///modules/sessionstore/PrivacyFilter.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "ScratchpadManager",
+  "resource:///modules/devtools/scratchpad-manager.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "SessionSaver",
+  "resource:///modules/sessionstore/SessionSaver.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "SessionCookies",
+  "resource:///modules/sessionstore/SessionCookies.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "SessionFile",
+  "resource:///modules/sessionstore/SessionFile.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "TabAttributes",
+  "resource:///modules/sessionstore/TabAttributes.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "TabState",
+  "resource:///modules/sessionstore/TabState.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "TabStateCache",
+  "resource:///modules/sessionstore/TabStateCache.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "Utils",
+  "resource:///modules/sessionstore/Utils.jsm");
+
+/**
+ * |true| if we are in debug mode, |false| otherwise.
+ * Debug mode is controlled by preference browser.sessionstore.debug
+ */
+let gDebuggingEnabled = false;
+function debug(aMsg) {
+  if (gDebuggingEnabled) {
+    aMsg = ("SessionStore: " + aMsg).replace(/\S{80}/g, "$&\n");
+    Services.console.logStringMessage(aMsg);
+  }
+}
+
+this.SessionStore = {
+  get promiseInitialized() {
+    return SessionStoreInternal.promiseInitialized;
+  },
+
+  get canRestoreLastSession() {
+    return SessionStoreInternal.canRestoreLastSession;
+  },
+
+  set canRestoreLastSession(val) {
+    SessionStoreInternal.canRestoreLastSession = val;
+  },
+
+  init: function ss_init() {
+    SessionStoreInternal.init();
+  },
+
+  getBrowserState: function ss_getBrowserState() {
+    return SessionStoreInternal.getBrowserState();
+  },
+
+  setBrowserState: function ss_setBrowserState(aState) {
+    SessionStoreInternal.setBrowserState(aState);
+  },
+
+  getWindowState: function ss_getWindowState(aWindow) {
+    return SessionStoreInternal.getWindowState(aWindow);
+  },
+
+  setWindowState: function ss_setWindowState(aWindow, aState, aOverwrite) {
+    SessionStoreInternal.setWindowState(aWindow, aState, aOverwrite);
+  },
+
+  getTabState: function ss_getTabState(aTab) {
+    return SessionStoreInternal.getTabState(aTab);
+  },
+
+  setTabState: function ss_setTabState(aTab, aState) {
+    SessionStoreInternal.setTabState(aTab, aState);
+  },
+
+  duplicateTab: function ss_duplicateTab(aWindow, aTab, aDelta = 0) {
+    return SessionStoreInternal.duplicateTab(aWindow, aTab, aDelta);
+  },
+
+  getClosedTabCount: function ss_getClosedTabCount(aWindow) {
+    return SessionStoreInternal.getClosedTabCount(aWindow);
+  },
+
+  getClosedTabData: function ss_getClosedTabDataAt(aWindow) {
+    return SessionStoreInternal.getClosedTabData(aWindow);
+  },
+
+  undoCloseTab: function ss_undoCloseTab(aWindow, aIndex) {
+    return SessionStoreInternal.undoCloseTab(aWindow, aIndex);
+  },
+
+  forgetClosedTab: function ss_forgetClosedTab(aWindow, aIndex) {
+    return SessionStoreInternal.forgetClosedTab(aWindow, aIndex);
+  },
+
+  getClosedWindowCount: function ss_getClosedWindowCount() {
+    return SessionStoreInternal.getClosedWindowCount();
+  },
+
+  getClosedWindowData: function ss_getClosedWindowData() {
+    return SessionStoreInternal.getClosedWindowData();
+  },
+
+  undoCloseWindow: function ss_undoCloseWindow(aIndex) {
+    return SessionStoreInternal.undoCloseWindow(aIndex);
+  },
+
+  forgetClosedWindow: function ss_forgetClosedWindow(aIndex) {
+    return SessionStoreInternal.forgetClosedWindow(aIndex);
+  },
+
+  getWindowValue: function ss_getWindowValue(aWindow, aKey) {
+    return SessionStoreInternal.getWindowValue(aWindow, aKey);
+  },
+
+  setWindowValue: function ss_setWindowValue(aWindow, aKey, aStringValue) {
+    SessionStoreInternal.setWindowValue(aWindow, aKey, aStringValue);
+  },
+
+  deleteWindowValue: function ss_deleteWindowValue(aWindow, aKey) {
+    SessionStoreInternal.deleteWindowValue(aWindow, aKey);
+  },
+
+  getTabValue: function ss_getTabValue(aTab, aKey) {
+    return SessionStoreInternal.getTabValue(aTab, aKey);
+  },
+
+  setTabValue: function ss_setTabValue(aTab, aKey, aStringValue) {
+    SessionStoreInternal.setTabValue(aTab, aKey, aStringValue);
+  },
+
+  deleteTabValue: function ss_deleteTabValue(aTab, aKey) {
+    SessionStoreInternal.deleteTabValue(aTab, aKey);
+  },
+
+  getGlobalValue: function ss_getGlobalValue(aKey) {
+    return SessionStoreInternal.getGlobalValue(aKey);
+  },
+
+  setGlobalValue: function ss_setGlobalValue(aKey, aStringValue) {
+    SessionStoreInternal.setGlobalValue(aKey, aStringValue);
+  },
+
+  deleteGlobalValue: function ss_deleteGlobalValue(aKey) {
+    SessionStoreInternal.deleteGlobalValue(aKey);
+  },
+
+  persistTabAttribute: function ss_persistTabAttribute(aName) {
+    SessionStoreInternal.persistTabAttribute(aName);
+  },
+
+  restoreLastSession: function ss_restoreLastSession() {
+    SessionStoreInternal.restoreLastSession();
+  },
+
+  getCurrentState: function (aUpdateAll) {
+    return SessionStoreInternal.getCurrentState(aUpdateAll);
+  },
+
+  /**
+   * Backstage pass to implementation details, used for testing purpose.
+   * Controlled by preference "browser.sessionstore.testmode".
+   */
+  get _internal() {
+    if (Services.prefs.getBoolPref("browser.sessionstore.debug")) {
+      return SessionStoreInternal;
+    }
+    return undefined;
+  },
+};
+
+// Freeze the SessionStore object. We don't want anyone to modify it.
+Object.freeze(SessionStore);
+
+let SessionStoreInternal = {
+  QueryInterface: XPCOMUtils.generateQI([
+    Ci.nsIDOMEventListener,
+    Ci.nsIObserver,
+    Ci.nsISupportsWeakReference
+  ]),
+
+  // set default load state
+  _loadState: STATE_STOPPED,
+
+  _globalState: new GlobalState(),
+
+  // During the initial restore and setBrowserState calls tracks the number of
+  // windows yet to be restored
+  _restoreCount: -1,
+
+  // This number gets incremented each time we start to restore a tab.
+  _nextRestoreEpoch: 1,
+
+  // For each <browser> element being restored, records the current epoch.
+  _browserEpochs: new WeakMap(),
+
+  // whether a setBrowserState call is in progress
+  _browserSetState: false,
+
+  // time in milliseconds when the session was started (saved across sessions),
+  // defaults to now if no session was restored or timestamp doesn't exist
+  _sessionStartTime: Date.now(),
+
+  // states for all currently opened windows
+  _windows: {},
+
+  // counter for creating unique window IDs
+  _nextWindowID: 0,
+
+  // states for all recently closed windows
+  _closedWindows: [],
+
+  // collection of session states yet to be restored
+  _statesToRestore: {},
+
+  // counts the number of crashes since the last clean start
+  _recentCrashes: 0,
+
+  // whether the last window was closed and should be restored
+  _restoreLastWindow: false,
+
+  // number of tabs currently restoring
+  _tabsRestoringCount: 0,
+
+  // When starting Firefox with a single private window, this is the place
+  // where we keep the session we actually wanted to restore in case the user
+  // decides to later open a non-private window as well.
+  _deferredInitialState: null,
+
+  // A promise resolved once initialization is complete
+  _deferredInitialized: Promise.defer(),
+
+  // Whether session has been initialized
+  _sessionInitialized: false,
+
+  // Promise that is resolved when we're ready to initialize
+  // and restore the session.
+  _promiseReadyForInitialization: null,
+
+  /**
+   * A promise fulfilled once initialization is complete.
+   */
+  get promiseInitialized() {
+    return this._deferredInitialized.promise;
+  },
+
+  get canRestoreLastSession() {
+    return LastSession.canRestore;
+  },
+
+  set canRestoreLastSession(val) {
+    // Cheat a bit; only allow false.
+    if (!val) {
+      LastSession.clear();
+    }
+  },
+
+  /**
+   * Initialize the sessionstore service.
+   */
+  init: function () {
+    if (this._initialized) {
+      throw new Error("SessionStore.init() must only be called once!");
+    }
+
+    TelemetryTimestamps.add("sessionRestoreInitialized");
+    OBSERVING.forEach(function(aTopic) {
+      Services.obs.addObserver(this, aTopic, true);
+    }, this);
+
+    this._initPrefs();
+    this._initialized = true;
+  },
+
+  /**
+   * Initialize the session using the state provided by SessionStartup
+   */
+  initSession: function () {
+    let state;
+    let ss = gSessionStartup;
+
+    try {
+      if (ss.doRestore() ||
+          ss.sessionType == Ci.nsISessionStartup.DEFER_SESSION)
+        state = ss.state;
+    }
+    catch(ex) { dump(ex + "\n"); } // no state to restore, which is ok
+
+    if (state) {
+      try {
+        // If we're doing a DEFERRED session, then we want to pull pinned tabs
+        // out so they can be restored.
+        if (ss.sessionType == Ci.nsISessionStartup.DEFER_SESSION) {
+          let [iniState, remainingState] = this._prepDataForDeferredRestore(state);
+          // If we have a iniState with windows, that means that we have windows
+          // with app tabs to restore.
+          if (iniState.windows.length)
+            state = iniState;
+          else
+            state = null;
+
+          if (remainingState.windows.length) {
+            LastSession.setState(remainingState);
+          }
+        }
+        else {
+          // Get the last deferred session in case the user still wants to
+          // restore it
+          LastSession.setState(state.lastSessionState);
+
+          if (ss.previousSessionCrashed) {
+            this._recentCrashes = (state.session &&
+                                   state.session.recentCrashes || 0) + 1;
+
+            if (this._needsRestorePage(state, this._recentCrashes)) {
+              // replace the crashed session with a restore-page-only session
+              let pageData = {
+                url: "about:sessionrestore",
+                formdata: {
+                  id: { "sessionData": state },
+                  xpath: {}
+                }
+              };
+              state = { windows: [{ tabs: [{ entries: [pageData] }] }] };
+            } else if (this._hasSingleTabWithURL(state.windows,
+                                                 "about:welcomeback")) {
+              // On a single about:welcomeback URL that crashed, replace about:welcomeback
+              // with about:sessionrestore, to make clear to the user that we crashed.
+              state.windows[0].tabs[0].entries[0].url = "about:sessionrestore";
+            }
+          }
+
+          // Update the session start time using the restored session state.
+          this._updateSessionStartTime(state);
+
+          // make sure that at least the first window doesn't have anything hidden
+          delete state.windows[0].hidden;
+          // Since nothing is hidden in the first window, it cannot be a popup
+          delete state.windows[0].isPopup;
+          // We don't want to minimize and then open a window at startup.
+          if (state.windows[0].sizemode == "minimized")
+            state.windows[0].sizemode = "normal";
+          // clear any lastSessionWindowID attributes since those don't matter
+          // during normal restore
+          state.windows.forEach(function(aWindow) {
+            delete aWindow.__lastSessionWindowID;
+          });
+        }
+      }
+      catch (ex) { debug("The session file is invalid: " + ex); }
+    }
+
+    // at this point, we've as good as resumed the session, so we can
+    // clear the resume_session_once flag, if it's set
+    if (this._loadState != STATE_QUITTING &&
+        this._prefBranch.getBoolPref("sessionstore.resume_session_once"))
+      this._prefBranch.setBoolPref("sessionstore.resume_session_once", false);
+
+    this._performUpgradeBackup();
+
+    return state;
+  },
+
+  /**
+   * If this is the first time we launc this build of Firefox,
+   * backup sessionstore.js.
+   */
+  _performUpgradeBackup: function ssi_performUpgradeBackup() {
+    // Perform upgrade backup, if necessary
+    const PREF_UPGRADE = "sessionstore.upgradeBackup.latestBuildID";
+
+    let buildID = Services.appinfo.platformBuildID;
+    let latestBackup = this._prefBranch.getCharPref(PREF_UPGRADE);
+    if (latestBackup == buildID) {
+      return Promise.resolve();
+    }
+    return Task.spawn(function task() {
+      try {
+        // Perform background backup
+        yield SessionFile.createBackupCopy("-" + buildID);
+
+        this._prefBranch.setCharPref(PREF_UPGRADE, buildID);
+
+        // In case of success, remove previous backup.
+        yield SessionFile.removeBackupCopy("-" + latestBackup);
+      } catch (ex) {
+        debug("Could not perform upgrade backup " + ex);
+        debug(ex.stack);
+      }
+    }.bind(this));
+  },
+
+  _initPrefs : function() {
+    this._prefBranch = Services.prefs.getBranch("browser.");
+
+    gDebuggingEnabled = this._prefBranch.getBoolPref("sessionstore.debug");
+
+    Services.prefs.addObserver("browser.sessionstore.debug", () => {
+      gDebuggingEnabled = this._prefBranch.getBoolPref("sessionstore.debug");
+    }, false);
+
+    this._max_tabs_undo = this._prefBranch.getIntPref("sessionstore.max_tabs_undo");
+    this._prefBranch.addObserver("sessionstore.max_tabs_undo", this, true);
+
+    this._max_windows_undo = this._prefBranch.getIntPref("sessionstore.max_windows_undo");
+    this._prefBranch.addObserver("sessionstore.max_windows_undo", this, true);
+  },
+
+  /**
+   * Called on application shutdown, after notifications:
+   * quit-application-granted, quit-application
+   */
+  _uninit: function ssi_uninit() {
+    if (!this._initialized) {
+      throw new Error("SessionStore is not initialized.");
+    }
+
+    // save all data for session resuming
+    if (this._sessionInitialized) {
+      SessionSaver.run();
+    }
+
+    // clear out priority queue in case it's still holding refs
+    TabRestoreQueue.reset();
+
+    // Make sure to cancel pending saves.
+    SessionSaver.cancel();
+  },
+
+  /**
+   * Handle notifications
+   */
+  observe: function ssi_observe(aSubject, aTopic, aData) {
+    switch (aTopic) {
+      case "domwindowopened": // catch new windows
+        this.onOpen(aSubject);
+        break;
+      case "domwindowclosed": // catch closed windows
+        this.onClose(aSubject);
+        break;
+      case "quit-application-requested":
+        this.onQuitApplicationRequested();
+        break;
+      case "quit-application-granted":
+        this.onQuitApplicationGranted();
+        break;
+      case "browser-lastwindow-close-granted":
+        this.onLastWindowCloseGranted();
+        break;
+      case "quit-application":
+        this.onQuitApplication(aData);
+        break;
+      case "browser:purge-session-history": // catch sanitization
+        this.onPurgeSessionHistory();
+        break;
+      case "browser:purge-domain-data":
+        this.onPurgeDomainData(aData);
+        break;
+      case "nsPref:changed": // catch pref changes
+        this.onPrefChange(aData);
+        break;
+      case "gather-telemetry":
+        this.onGatherTelemetry();
+        break;
+    }
+  },
+
+  /**
+   * This method handles incoming messages sent by the session store content
+   * script and thus enables communication with OOP tabs.
+   */
+  receiveMessage: function ssi_receiveMessage(aMessage) {
+    var browser = aMessage.target;
+    var win = browser.ownerDocument.defaultView;
+    let tab = this._getTabForBrowser(browser);
+    if (!tab) {
+      // Ignore messages from <browser> elements that are not tabs.
+      return;
+    }
+
+    switch (aMessage.name) {
+      case "SessionStore:setupSyncHandler":
+        TabState.setSyncHandler(browser, aMessage.objects.handler);
+        break;
+      case "SessionStore:update":
+        this.recordTelemetry(aMessage.data.telemetry);
+        TabState.update(browser, aMessage.data);
+        this.saveStateDelayed(win);
+        break;
+      case "SessionStore:restoreHistoryComplete":
+        if (this.isCurrentEpoch(browser, aMessage.data.epoch)) {
+          // Notify the tabbrowser that the tab chrome has been restored.
+          let tabData = browser.__SS_data;
+
+          // wall-paper fix for bug 439675: make sure that the URL to be loaded
+          // is always visible in the address bar
+          let activePageData = tabData.entries[tabData.index - 1] || null;
+          let uri = activePageData ? activePageData.url || null : null;
+          browser.userTypedValue = uri;
+
+          // If the page has a title, set it.
+          if (activePageData) {
+            if (activePageData.title) {
+              tab.label = activePageData.title;
+              tab.crop = "end";
+            } else if (activePageData.url != "about:blank") {
+              tab.label = activePageData.url;
+              tab.crop = "center";
+            }
+          }
+
+          // Restore the tab icon.
+          if ("image" in tabData) {
+            win.gBrowser.setIcon(tab, tabData.image);
+          }
+
+          let event = win.document.createEvent("Events");
+          event.initEvent("SSTabRestoring", true, false);
+          tab.dispatchEvent(event);
+        }
+        break;
+      case "SessionStore:restoreTabContentStarted":
+        if (this.isCurrentEpoch(browser, aMessage.data.epoch)) {
+          // If the user was typing into the URL bar when we crashed, but hadn't hit
+          // enter yet, then we just need to write that value to the URL bar without
+          // loading anything. This must happen after the load, since it will clear
+          // userTypedValue.
+          let tabData = browser.__SS_data;
+          if (tabData.userTypedValue && !tabData.userTypedClear) {
+            browser.userTypedValue = tabData.userTypedValue;
+            win.URLBarSetURI();
+          }
+        }
+        break;
+      case "SessionStore:restoreTabContentComplete":
+        if (this.isCurrentEpoch(browser, aMessage.data.epoch)) {
+          // This callback is used exclusively by tests that want to
+          // monitor the progress of network loads.
+          if (gDebuggingEnabled) {
+            Services.obs.notifyObservers(browser, NOTIFY_TAB_RESTORED, null);
+          }
+
+          if (tab) {
+            SessionStoreInternal._resetLocalTabRestoringState(tab);
+            SessionStoreInternal.restoreNextTab();
+          }
+        }
+        break;
+      case "SessionStore:restoreDocumentComplete":
+        if (this.isCurrentEpoch(browser, aMessage.data.epoch)) {
+          // Document has been restored. Delete all the state associated
+          // with it and trigger SSTabRestored.
+          let tab = browser.__SS_restore_tab;
+
+          delete browser.__SS_restore_data;
+          delete browser.__SS_restore_tab;
+          delete browser.__SS_data;
+
+          this._sendTabRestoredNotification(tab);
+        }
+        break;
+      case "SessionStore:reloadPendingTab":
+        if (this.isCurrentEpoch(browser, aMessage.data.epoch)) {
+          if (tab && browser.__SS_restoreState == TAB_STATE_NEEDS_RESTORE) {
+            this.restoreTabContent(tab);
+          }
+        }
+        break;
+      default:
+        debug("received unknown message '" + aMessage.name + "'");
+        break;
+    }
+  },
+
+  /**
+   * Record telemetry measurements stored in an object.
+   * @param telemetry
+   *        {histogramID: value, ...} An object mapping histogramIDs to the
+   *        value to be recorded for that ID,
+   */
+  recordTelemetry: function (telemetry) {
+    for (let histogramId in telemetry){
+      Telemetry.getHistogramById(histogramId).add(telemetry[histogramId]);
+    }
+  },
+
+  /* ........ Window Event Handlers .............. */
+
+  /**
+   * Implement nsIDOMEventListener for handling various window and tab events
+   */
+  handleEvent: function ssi_handleEvent(aEvent) {
+    var win = aEvent.currentTarget.ownerDocument.defaultView;
+    let browser;
+    switch (aEvent.type) {
+      case "TabOpen":
+        this.onTabAdd(win, aEvent.originalTarget);
+        break;
+      case "TabClose":
+        // aEvent.detail determines if the tab was closed by moving to a different window
+        if (!aEvent.detail)
+          this.onTabClose(win, aEvent.originalTarget);
+        this.onTabRemove(win, aEvent.originalTarget);
+        break;
+      case "TabSelect":
+        this.onTabSelect(win);
+        break;
+      case "TabShow":
+        this.onTabShow(win, aEvent.originalTarget);
+        break;
+      case "TabHide":
+        this.onTabHide(win, aEvent.originalTarget);
+        break;
+      case "TabPinned":
+      case "TabUnpinned":
+        this.saveStateDelayed(win);
+        break;
+    }
+    this._clearRestoringWindows();
+  },
+
+  /**
+   * Generate a unique window identifier
+   * @return string
+   *         A unique string to identify a window
+   */
+  _generateWindowID: function ssi_generateWindowID() {
+    return "window" + (this._nextWindowID++);
+  },
+
+  /**
+   * If it's the first window load since app start...
+   * - determine if we're reloading after a crash or a forced-restart
+   * - restore window state
+   * - restart downloads
+   * Set up event listeners for this window's tabs
+   * @param aWindow
+   *        Window reference
+   * @param aInitialState
+   *        The initial state to be loaded after startup (optional)
+   */
+  onLoad: function ssi_onLoad(aWindow, aInitialState = null) {
+    // return if window has already been initialized
+    if (aWindow && aWindow.__SSi && this._windows[aWindow.__SSi])
+      return;
+
+    // ignore windows opened while shutting down
+    if (this._loadState == STATE_QUITTING)
+      return;
+
+    // Assign the window a unique identifier we can use to reference
+    // internal data about the window.
+    aWindow.__SSi = this._generateWindowID();
+
+    let mm = aWindow.messageManager;
+    MESSAGES.forEach(msg => mm.addMessageListener(msg, this));
+
+    // Load the frame script after registering listeners.
+    mm.loadFrameScript("chrome://browser/content/content-sessionStore.js", true);
+
+    // and create its data object
+    this._windows[aWindow.__SSi] = { tabs: [], selected: 0, _closedTabs: [], busy: false };
+
+    let isPrivateWindow = false;
+    if (PrivateBrowsingUtils.isWindowPrivate(aWindow))
+      this._windows[aWindow.__SSi].isPrivate = isPrivateWindow = true;
+    if (!this._isWindowLoaded(aWindow))
+      this._windows[aWindow.__SSi]._restoring = true;
+    if (!aWindow.toolbar.visible)
+      this._windows[aWindow.__SSi].isPopup = true;
+
+    // perform additional initialization when the first window is loading
+    if (this._loadState == STATE_STOPPED) {
+      this._loadState = STATE_RUNNING;
+      SessionSaver.updateLastSaveTime();
+
+      // restore a crashed session resp. resume the last session if requested
+      if (aInitialState) {
+        if (isPrivateWindow) {
+          // We're starting with a single private window. Save the state we
+          // actually wanted to restore so that we can do it later in case
+          // the user opens another, non-private window.
+          this._deferredInitialState = gSessionStartup.state;
+
+          // Nothing to restore now, notify observers things are complete.
+          Services.obs.notifyObservers(null, NOTIFY_WINDOWS_RESTORED, "");
+        } else {
+          TelemetryTimestamps.add("sessionRestoreRestoring");
+          this._restoreCount = aInitialState.windows ? aInitialState.windows.length : 0;
+
+          // global data must be restored before restoreWindow is called so that
+          // it happens before observers are notified
+          this._globalState.setFromState(aInitialState);
+
+          let overwrite = this._isCmdLineEmpty(aWindow, aInitialState);
+          let options = {firstWindow: true, overwriteTabs: overwrite};
+          this.restoreWindow(aWindow, aInitialState, options);
+        }
+      }
+      else {
+        // Nothing to restore, notify observers things are complete.
+        Services.obs.notifyObservers(null, NOTIFY_WINDOWS_RESTORED, "");
+
+        // The next delayed save request should execute immediately.
+        SessionSaver.clearLastSaveTime();
+      }
+    }
+    // this window was opened by _openWindowWithState
+    else if (!this._isWindowLoaded(aWindow)) {
+      let state = this._statesToRestore[aWindow.__SS_restoreID];
+      let options = {overwriteTabs: true, isFollowUp: state.windows.length == 1};
+      this.restoreWindow(aWindow, state, options);
+    }
+    // The user opened another, non-private window after starting up with
+    // a single private one. Let's restore the session we actually wanted to
+    // restore at startup.
+    else if (this._deferredInitialState && !isPrivateWindow &&
+             aWindow.toolbar.visible) {
+
+      // global data must be restored before restoreWindow is called so that
+      // it happens before observers are notified
+      this._globalState.setFromState(this._deferredInitialState);
+
+      this._restoreCount = this._deferredInitialState.windows ?
+        this._deferredInitialState.windows.length : 0;
+      this.restoreWindow(aWindow, this._deferredInitialState, {firstWindow: true});
+      this._deferredInitialState = null;
+    }
+    else if (this._restoreLastWindow && aWindow.toolbar.visible &&
+             this._closedWindows.length && !isPrivateWindow) {
+
+      // default to the most-recently closed window
+      // don't use popup windows
+      let closedWindowState = null;
+      let closedWindowIndex;
+      for (let i = 0; i < this._closedWindows.length; i++) {
+        // Take the first non-popup, point our object at it, and break out.
+        if (!this._closedWindows[i].isPopup) {
+          closedWindowState = this._closedWindows[i];
+          closedWindowIndex = i;
+          break;
+        }
+      }
+
+      if (closedWindowState) {
+        let newWindowState;
+#ifndef XP_MACOSX
+        if (!this._doResumeSession()) {
+#endif
+          // We want to split the window up into pinned tabs and unpinned tabs.
+          // Pinned tabs should be restored. If there are any remaining tabs,
+          // they should be added back to _closedWindows.
+          // We'll cheat a little bit and reuse _prepDataForDeferredRestore
+          // even though it wasn't built exactly for this.
+          let [appTabsState, normalTabsState] =
+            this._prepDataForDeferredRestore({ windows: [closedWindowState] });
+
+          // These are our pinned tabs, which we should restore
+          if (appTabsState.windows.length) {
+            newWindowState = appTabsState.windows[0];
+            delete newWindowState.__lastSessionWindowID;
+          }
+
+          // In case there were no unpinned tabs, remove the window from _closedWindows
+          if (!normalTabsState.windows.length) {
+            this._closedWindows.splice(closedWindowIndex, 1);
+          }
+          // Or update _closedWindows with the modified state
+          else {
+            delete normalTabsState.windows[0].__lastSessionWindowID;
+            this._closedWindows[closedWindowIndex] = normalTabsState.windows[0];
+          }
+#ifndef XP_MACOSX
+        }
+        else {
+          // If we're just restoring the window, make sure it gets removed from
+          // _closedWindows.
+          this._closedWindows.splice(closedWindowIndex, 1);
+          newWindowState = closedWindowState;
+          delete newWindowState.hidden;
+        }
+#endif
+        if (newWindowState) {
+          // Ensure that the window state isn't hidden
+          this._restoreCount = 1;
+          let state = { windows: [newWindowState] };
+          let options = {overwriteTabs: this._isCmdLineEmpty(aWindow, state)};
+          this.restoreWindow(aWindow, state, options);
+        }
+      }
+      // we actually restored the session just now.
+      this._prefBranch.setBoolPref("sessionstore.resume_session_once", false);
+    }
+    if (this._restoreLastWindow && aWindow.toolbar.visible) {
+      // always reset (if not a popup window)
+      // we don't want to restore a window directly after, for example,
+      // undoCloseWindow was executed.
+      this._restoreLastWindow = false;
+    }
+
+    var tabbrowser = aWindow.gBrowser;
+
+    // add tab change listeners to all already existing tabs
+    for (let i = 0; i < tabbrowser.tabs.length; i++) {
+      this.onTabAdd(aWindow, tabbrowser.tabs[i], true);
+    }
+    // notification of tab add/remove/selection/show/hide
+    TAB_EVENTS.forEach(function(aEvent) {
+      tabbrowser.tabContainer.addEventListener(aEvent, this, true);
+    }, this);
+  },
+
+  /**
+   * On window open
+   * @param aWindow
+   *        Window reference
+   */
+  onOpen: function ssi_onOpen(aWindow) {
+    let onload = () => {
+      aWindow.removeEventListener("load", onload);
+
+      let windowType = aWindow.document.documentElement.getAttribute("windowtype");
+
+      // Ignore non-browser windows.
+      if (windowType != "navigator:browser") {
+        return;
+      }
+
+      if (this._sessionInitialized) {
+        this.onLoad(aWindow);
+        return;
+      }
+
+      // The very first window that is opened creates a promise that is then
+      // re-used by all subsequent windows. The promise will be used to tell
+      // when we're ready for initialization.
+      if (!this._promiseReadyForInitialization) {
+        let deferred = Promise.defer();
+
+        // Wait for the given window's delayed startup to be finished.
+        Services.obs.addObserver(function obs(subject, topic) {
+          if (aWindow == subject) {
+            Services.obs.removeObserver(obs, topic);
+            deferred.resolve();
+          }
+        }, "browser-delayed-startup-finished", false);
+
+        // We are ready for initialization as soon as the session file has been
+        // read from disk and the initial window's delayed startup has finished.
+        this._promiseReadyForInitialization =
+          Promise.all([deferred.promise, gSessionStartup.onceInitialized]);
+      }
+
+      // We can't call this.onLoad since initialization
+      // hasn't completed, so we'll wait until it is done.
+      // Even if additional windows are opened and wait
+      // for initialization as well, the first opened
+      // window should execute first, and this.onLoad
+      // will be called with the initialState.
+      this._promiseReadyForInitialization.then(() => {
+        if (aWindow.closed) {
+          return;
+        }
+
+        if (this._sessionInitialized) {
+          this.onLoad(aWindow);
+        } else {
+          let initialState = this.initSession();
+          this._sessionInitialized = true;
+          this.onLoad(aWindow, initialState);
+
+          // Let everyone know we're done.
+          this._deferredInitialized.resolve();
+        }
+      }, console.error);
+    };
+
+    aWindow.addEventListener("load", onload);
+  },
+
+  /**
+   * On window close...
+   * - remove event listeners from tabs
+   * - save all window data
+   * @param aWindow
+   *        Window reference
+   */
+  onClose: function ssi_onClose(aWindow) {
+    // this window was about to be restored - conserve its original data, if any
+    let isFullyLoaded = this._isWindowLoaded(aWindow);
+    if (!isFullyLoaded) {
+      if (!aWindow.__SSi) {
+        aWindow.__SSi = this._generateWindowID();
+      }
+
+      this._windows[aWindow.__SSi] = this._statesToRestore[aWindow.__SS_restoreID];
+      delete this._statesToRestore[aWindow.__SS_restoreID];
+      delete aWindow.__SS_restoreID;
+    }
+
+    // ignore windows not tracked by SessionStore
+    if (!aWindow.__SSi || !this._windows[aWindow.__SSi]) {
+      return;
+    }
+
+    // notify that the session store will stop tracking this window so that
+    // extensions can store any data about this window in session store before
+    // that's not possible anymore
+    let event = aWindow.document.createEvent("Events");
+    event.initEvent("SSWindowClosing", true, false);
+    aWindow.dispatchEvent(event);
+
+    if (this.windowToFocus && this.windowToFocus == aWindow) {
+      delete this.windowToFocus;
+    }
+
+    var tabbrowser = aWindow.gBrowser;
+
+    TAB_EVENTS.forEach(function(aEvent) {
+      tabbrowser.tabContainer.removeEventListener(aEvent, this, true);
+    }, this);
+
+    let winData = this._windows[aWindow.__SSi];
+
+    // Collect window data only when *not* closed during shutdown.
+    if (this._loadState == STATE_RUNNING) {
+      // Flush all data queued in the content script before the window is gone.
+      TabState.flushWindow(aWindow);
+
+      // update all window data for a last time
+      this._collectWindowData(aWindow);
+
+      if (isFullyLoaded) {
+        winData.title = aWindow.content.document.title || tabbrowser.selectedTab.label;
+        winData.title = this._replaceLoadingTitle(winData.title, tabbrowser,
+                                                  tabbrowser.selectedTab);
+        SessionCookies.update([winData]);
+      }
+
+#ifndef XP_MACOSX
+      // Until we decide otherwise elsewhere, this window is part of a series
+      // of closing windows to quit.
+      winData._shouldRestore = true;
+#endif
+
+      // Store the window's close date to figure out when each individual tab
+      // was closed. This timestamp should allow re-arranging data based on how
+      // recently something was closed.
+      winData.closedAt = Date.now();
+
+      // Save non-private windows if they have at
+      // least one saveable tab or are the last window.
+      if (!winData.isPrivate) {
+        // Remove any open private tabs the window may contain.
+        PrivacyFilter.filterPrivateTabs(winData);
+
+        // Determine whether the window has any tabs worth saving.
+        let hasSaveableTabs = winData.tabs.some(this._shouldSaveTabState);
+
+        // When closing windows one after the other until Firefox quits, we
+        // will move those closed in series back to the "open windows" bucket
+        // before writing to disk. If however there is only a single window
+        // with tabs we deem not worth saving then we might end up with a
+        // random closed or even a pop-up window re-opened. To prevent that
+        // we explicitly allow saving an "empty" window state.
+        let isLastWindow =
+          Object.keys(this._windows).length == 1 &&
+          !this._closedWindows.some(win => win._shouldRestore || false);
+
+        if (hasSaveableTabs || isLastWindow) {
+          // we don't want to save the busy state
+          delete winData.busy;
+
+          this._closedWindows.unshift(winData);
+          this._capClosedWindows();
+        }
+      }
+
+      // clear this window from the list
+      delete this._windows[aWindow.__SSi];
+
+      // save the state without this window to disk
+      this.saveStateDelayed();
+    }
+
+    for (let i = 0; i < tabbrowser.tabs.length; i++) {
+      this.onTabRemove(aWindow, tabbrowser.tabs[i], true);
+    }
+
+    // Cache the window state until it is completely gone.
+    DyingWindowCache.set(aWindow, winData);
+
+    let mm = aWindow.messageManager;
+    MESSAGES.forEach(msg => mm.removeMessageListener(msg, this));
+
+    delete aWindow.__SSi;
+  },
+
+  /**
+   * On quit application requested
+   */
+  onQuitApplicationRequested: function ssi_onQuitApplicationRequested() {
+    // get a current snapshot of all windows
+    this._forEachBrowserWindow(function(aWindow) {
+      // Flush all data queued in the content script to not lose it when
+      // shutting down.
+      TabState.flushWindow(aWindow);
+      this._collectWindowData(aWindow);
+    });
+    // we must cache this because _getMostRecentBrowserWindow will always
+    // return null by the time quit-application occurs
+    var activeWindow = this._getMostRecentBrowserWindow();
+    if (activeWindow)
+      this.activeWindowSSiCache = activeWindow.__SSi || "";
+    DirtyWindows.clear();
+  },
+
+  /**
+   * On quit application granted
+   */
+  onQuitApplicationGranted: function ssi_onQuitApplicationGranted() {
+    // freeze the data at what we've got (ignoring closing windows)
+    this._loadState = STATE_QUITTING;
+  },
+
+  /**
+   * On last browser window close
+   */
+  onLastWindowCloseGranted: function ssi_onLastWindowCloseGranted() {
+    // last browser window is quitting.
+    // remember to restore the last window when another browser window is opened
+    // do not account for pref(resume_session_once) at this point, as it might be
+    // set by another observer getting this notice after us
+    this._restoreLastWindow = true;
+  },
+
+  /**
+   * On quitting application
+   * @param aData
+   *        String type of quitting
+   */
+  onQuitApplication: function ssi_onQuitApplication(aData) {
+    if (aData == "restart") {
+      this._prefBranch.setBoolPref("sessionstore.resume_session_once", true);
+      // The browser:purge-session-history notification fires after the
+      // quit-application notification so unregister the
+      // browser:purge-session-history notification to prevent clearing
+      // session data on disk on a restart.  It is also unnecessary to
+      // perform any other sanitization processing on a restart as the
+      // browser is about to exit anyway.
+      Services.obs.removeObserver(this, "browser:purge-session-history");
+    }
+
+    if (aData != "restart") {
+      // Throw away the previous session on shutdown
+      LastSession.clear();
+    }
+
+    this._loadState = STATE_QUITTING; // just to be sure
+    this._uninit();
+  },
+
+  /**
+   * On purge of session history
+   */
+  onPurgeSessionHistory: function ssi_onPurgeSessionHistory() {
+    SessionFile.wipe();
+    // If the browser is shutting down, simply return after clearing the
+    // session data on disk as this notification fires after the
+    // quit-application notification so the browser is about to exit.
+    if (this._loadState == STATE_QUITTING)
+      return;
+    LastSession.clear();
+    let openWindows = {};
+    this._forEachBrowserWindow(function(aWindow) {
+      Array.forEach(aWindow.gBrowser.tabs, function(aTab) {
+        delete aTab.linkedBrowser.__SS_data;
+        if (aTab.linkedBrowser.__SS_restoreState)
+          this._resetTabRestoringState(aTab);
+      }, this);
+      openWindows[aWindow.__SSi] = true;
+    });
+    // also clear all data about closed tabs and windows
+    for (let ix in this._windows) {
+      if (ix in openWindows) {
+        this._windows[ix]._closedTabs = [];
+      } else {
+        delete this._windows[ix];
+      }
+    }
+    // also clear all data about closed windows
+    this._closedWindows = [];
+    // give the tabbrowsers a chance to clear their histories first
+    var win = this._getMostRecentBrowserWindow();
+    if (win) {
+      win.setTimeout(() => SessionSaver.run(), 0);
+    } else if (this._loadState == STATE_RUNNING) {
+      SessionSaver.run();
+    }
+
+    this._clearRestoringWindows();
+  },
+
+  /**
+   * On purge of domain data
+   * @param aData
+   *        String domain data
+   */
+  onPurgeDomainData: function ssi_onPurgeDomainData(aData) {
+    // does a session history entry contain a url for the given domain?
+    function containsDomain(aEntry) {
+      if (Utils.hasRootDomain(aEntry.url, aData)) {
+        return true;
+      }
+      return aEntry.children && aEntry.children.some(containsDomain, this);
+    }
+    // remove all closed tabs containing a reference to the given domain
+    for (let ix in this._windows) {
+      let closedTabs = this._windows[ix]._closedTabs;
+      for (let i = closedTabs.length - 1; i >= 0; i--) {
+        if (closedTabs[i].state.entries.some(containsDomain, this))
+          closedTabs.splice(i, 1);
+      }
+    }
+    // remove all open & closed tabs containing a reference to the given
+    // domain in closed windows
+    for (let ix = this._closedWindows.length - 1; ix >= 0; ix--) {
+      let closedTabs = this._closedWindows[ix]._closedTabs;
+      let openTabs = this._closedWindows[ix].tabs;
+      let openTabCount = openTabs.length;
+      for (let i = closedTabs.length - 1; i >= 0; i--)
+        if (closedTabs[i].state.entries.some(containsDomain, this))
+          closedTabs.splice(i, 1);
+      for (let j = openTabs.length - 1; j >= 0; j--) {
+        if (openTabs[j].entries.some(containsDomain, this)) {
+          openTabs.splice(j, 1);
+          if (this._closedWindows[ix].selected > j)
+            this._closedWindows[ix].selected--;
+        }
+      }
+      if (openTabs.length == 0) {
+        this._closedWindows.splice(ix, 1);
+      }
+      else if (openTabs.length != openTabCount) {
+        // Adjust the window's title if we removed an open tab
+        let selectedTab = openTabs[this._closedWindows[ix].selected - 1];
+        // some duplication from restoreHistory - make sure we get the correct title
+        let activeIndex = (selectedTab.index || selectedTab.entries.length) - 1;
+        if (activeIndex >= selectedTab.entries.length)
+          activeIndex = selectedTab.entries.length - 1;
+        this._closedWindows[ix].title = selectedTab.entries[activeIndex].title;
+      }
+    }
+
+    if (this._loadState == STATE_RUNNING) {
+      SessionSaver.run();
+    }
+
+    this._clearRestoringWindows();
+  },
+
+  /**
+   * On preference change
+   * @param aData
+   *        String preference changed
+   */
+  onPrefChange: function ssi_onPrefChange(aData) {
+    switch (aData) {
+      // if the user decreases the max number of closed tabs they want
+      // preserved update our internal states to match that max
+      case "sessionstore.max_tabs_undo":
+        this._max_tabs_undo = this._prefBranch.getIntPref("sessionstore.max_tabs_undo");
+        for (let ix in this._windows) {
+          this._windows[ix]._closedTabs.splice(this._max_tabs_undo, this._windows[ix]._closedTabs.length);
+        }
+        break;
+      case "sessionstore.max_windows_undo":
+        this._max_windows_undo = this._prefBranch.getIntPref("sessionstore.max_windows_undo");
+        this._capClosedWindows();
+        break;
+    }
+  },
+
+  /**
+   * set up listeners for a new tab
+   * @param aWindow
+   *        Window reference
+   * @param aTab
+   *        Tab reference
+   * @param aNoNotification
+   *        bool Do not save state if we're updating an existing tab
+   */
+  onTabAdd: function ssi_onTabAdd(aWindow, aTab, aNoNotification) {
+    if (!aNoNotification) {
+      this.saveStateDelayed(aWindow);
+    }
+  },
+
+  /**
+   * remove listeners for a tab
+   * @param aWindow
+   *        Window reference
+   * @param aTab
+   *        Tab reference
+   * @param aNoNotification
+   *        bool Do not save state if we're updating an existing tab
+   */
+  onTabRemove: function ssi_onTabRemove(aWindow, aTab, aNoNotification) {
+    let browser = aTab.linkedBrowser;
+    delete browser.__SS_data;
+
+    // If this tab was in the middle of restoring or still needs to be restored,
+    // we need to reset that state. If the tab was restoring, we will attempt to
+    // restore the next tab.
+    let previousState = browser.__SS_restoreState;
+    if (previousState) {
+      this._resetTabRestoringState(aTab);
+      if (previousState == TAB_STATE_RESTORING)
+        this.restoreNextTab();
+    }
+
+    if (!aNoNotification) {
+      this.saveStateDelayed(aWindow);
+    }
+  },
+
+  /**
+   * When a tab closes, collect its properties
+   * @param aWindow
+   *        Window reference
+   * @param aTab
+   *        Tab reference
+   */
+  onTabClose: function ssi_onTabClose(aWindow, aTab) {
+    // notify the tabbrowser that the tab state will be retrieved for the last time
+    // (so that extension authors can easily set data on soon-to-be-closed tabs)
+    var event = aWindow.document.createEvent("Events");
+    event.initEvent("SSTabClosing", true, false);
+    aTab.dispatchEvent(event);
+
+    // don't update our internal state if we don't have to
+    if (this._max_tabs_undo == 0) {
+      return;
+    }
+
+    // Flush all data queued in the content script before the tab is gone.
+    TabState.flush(aTab.linkedBrowser);
+
+    // Get the latest data for this tab (generally, from the cache)
+    let tabState = TabState.collect(aTab);
+
+    // Don't save private tabs
+    let isPrivateWindow = PrivateBrowsingUtils.isWindowPrivate(aWindow);
+    if (!isPrivateWindow && tabState.isPrivate) {
+      return;
+    }
+
+    // store closed-tab data for undo
+    if (this._shouldSaveTabState(tabState)) {
+      let tabTitle = aTab.label;
+      let tabbrowser = aWindow.gBrowser;
+      tabTitle = this._replaceLoadingTitle(tabTitle, tabbrowser, aTab);
+
+      this._windows[aWindow.__SSi]._closedTabs.unshift({
+        state: tabState,
+        title: tabTitle,
+        image: tabbrowser.getIcon(aTab),
+        pos: aTab._tPos,
+        closedAt: Date.now()
+      });
+      var length = this._windows[aWindow.__SSi]._closedTabs.length;
+      if (length > this._max_tabs_undo)
+        this._windows[aWindow.__SSi]._closedTabs.splice(this._max_tabs_undo, length - this._max_tabs_undo);
+    }
+  },
+
+  /**
+   * When a tab is selected, save session data
+   * @param aWindow
+   *        Window reference
+   */
+  onTabSelect: function ssi_onTabSelect(aWindow) {
+    if (this._loadState == STATE_RUNNING) {
+      this._windows[aWindow.__SSi].selected = aWindow.gBrowser.tabContainer.selectedIndex;
+
+      let tab = aWindow.gBrowser.selectedTab;
+      // If __SS_restoreState is still on the browser and it is
+      // TAB_STATE_NEEDS_RESTORE, then then we haven't restored
+      // this tab yet. Explicitly call restoreTabContent to kick off the restore.
+      if (tab.linkedBrowser.__SS_restoreState &&
+          tab.linkedBrowser.__SS_restoreState == TAB_STATE_NEEDS_RESTORE)
+        this.restoreTabContent(tab);
+    }
+  },
+
+  onTabShow: function ssi_onTabShow(aWindow, aTab) {
+    // If the tab hasn't been restored yet, move it into the right bucket
+    if (aTab.linkedBrowser.__SS_restoreState &&
+        aTab.linkedBrowser.__SS_restoreState == TAB_STATE_NEEDS_RESTORE) {
+      TabRestoreQueue.hiddenToVisible(aTab);
+
+      // let's kick off tab restoration again to ensure this tab gets restored
+      // with "restore_hidden_tabs" == false (now that it has become visible)
+      this.restoreNextTab();
+    }
+
+    // Default delay of 2 seconds gives enough time to catch multiple TabShow
+    // events due to changing groups in Panorama.
+    this.saveStateDelayed(aWindow);
+  },
+
+  onTabHide: function ssi_onTabHide(aWindow, aTab) {
+    // If the tab hasn't been restored yet, move it into the right bucket
+    if (aTab.linkedBrowser.__SS_restoreState &&
+        aTab.linkedBrowser.__SS_restoreState == TAB_STATE_NEEDS_RESTORE) {
+      TabRestoreQueue.visibleToHidden(aTab);
+    }
+
+    // Default delay of 2 seconds gives enough time to catch multiple TabHide
+    // events due to changing groups in Panorama.
+    this.saveStateDelayed(aWindow);
+  },
+
+  onGatherTelemetry: function() {
+    // On the first gather-telemetry notification of the session,
+    // gather telemetry data.
+    Services.obs.removeObserver(this, "gather-telemetry");
+    let stateString = SessionStore.getBrowserState();
+    return SessionFile.gatherTelemetry(stateString);
+  },
+
+  /* ........ nsISessionStore API .............. */
+
+  getBrowserState: function ssi_getBrowserState() {
+    let state = this.getCurrentState();
+
+    // Don't include the last session state in getBrowserState().
+    delete state.lastSessionState;
+
+    // Don't include any deferred initial state.
+    delete state.deferredInitialState;
+
+    return this._toJSONString(state);
+  },
+
+  setBrowserState: function ssi_setBrowserState(aState) {
+    this._handleClosedWindows();
+
+    try {
+      var state = JSON.parse(aState);
+    }
+    catch (ex) { /* invalid state object - don't restore anything */ }
+    if (!state) {
+      throw Components.Exception("Invalid state string: not JSON", Cr.NS_ERROR_INVALID_ARG);
+    }
+    if (!state.windows) {
+      throw Components.Exception("No windows", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    this._browserSetState = true;
+
+    // Make sure the priority queue is emptied out
+    this._resetRestoringState();
+
+    var window = this._getMostRecentBrowserWindow();
+    if (!window) {
+      this._restoreCount = 1;
+      this._openWindowWithState(state);
+      return;
+    }
+
+    // close all other browser windows
+    this._forEachBrowserWindow(function(aWindow) {
+      if (aWindow != window) {
+        aWindow.close();
+        this.onClose(aWindow);
+      }
+    });
+
+    // make sure closed window data isn't kept
+    this._closedWindows = [];
+
+    // determine how many windows are meant to be restored
+    this._restoreCount = state.windows ? state.windows.length : 0;
+
+    // global data must be restored before restoreWindow is called so that
+    // it happens before observers are notified
+    this._globalState.setFromState(state);
+
+    // restore to the given state
+    this.restoreWindow(window, state, {overwriteTabs: true});
+  },
+
+  getWindowState: function ssi_getWindowState(aWindow) {
+    if ("__SSi" in aWindow) {
+      return this._toJSONString(this._getWindowState(aWindow));
+    }
+
+    if (DyingWindowCache.has(aWindow)) {
+      let data = DyingWindowCache.get(aWindow);
+      return this._toJSONString({ windows: [data] });
+    }
+
+    throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
+  },
+
+  setWindowState: function ssi_setWindowState(aWindow, aState, aOverwrite) {
+    if (!aWindow.__SSi) {
+      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    this.restoreWindow(aWindow, aState, {overwriteTabs: aOverwrite});
+  },
+
+  getTabState: function ssi_getTabState(aTab) {
+    if (!aTab.ownerDocument) {
+      throw Components.Exception("Invalid tab object: no ownerDocument", Cr.NS_ERROR_INVALID_ARG);
+    }
+    if (!aTab.ownerDocument.defaultView.__SSi) {
+      throw Components.Exception("Default view is not tracked", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    let tabState = TabState.collect(aTab);
+
+    return this._toJSONString(tabState);
+  },
+
+  setTabState: function ssi_setTabState(aTab, aState) {
+    // Remove the tab state from the cache.
+    // Note that we cannot simply replace the contents of the cache
+    // as |aState| can be an incomplete state that will be completed
+    // by |restoreTabs|.
+    let tabState = JSON.parse(aState);
+    if (!tabState) {
+      throw Components.Exception("Invalid state string: not JSON", Cr.NS_ERROR_INVALID_ARG);
+    }
+    if (typeof tabState != "object") {
+      throw Components.Exception("Not an object", Cr.NS_ERROR_INVALID_ARG);
+    }
+    if (!("entries" in tabState)) {
+      throw Components.Exception("Invalid state object: no entries", Cr.NS_ERROR_INVALID_ARG);
+    }
+    if (!aTab.ownerDocument) {
+      throw Components.Exception("Invalid tab object: no ownerDocument", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    let window = aTab.ownerDocument.defaultView;
+    if (!("__SSi" in window)) {
+      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    if (aTab.linkedBrowser.__SS_restoreState) {
+      this._resetTabRestoringState(aTab);
+    }
+
+    this._setWindowStateBusy(window);
+    this.restoreTabs(window, [aTab], [tabState], 0);
+  },
+
+  duplicateTab: function ssi_duplicateTab(aWindow, aTab, aDelta = 0) {
+    if (!aTab.ownerDocument) {
+      throw Components.Exception("Invalid tab object: no ownerDocument", Cr.NS_ERROR_INVALID_ARG);
+    }
+    if (!aTab.ownerDocument.defaultView.__SSi) {
+      throw Components.Exception("Default view is not tracked", Cr.NS_ERROR_INVALID_ARG);
+    }
+    if (!aWindow.getBrowser) {
+      throw Components.Exception("Invalid window object: no getBrowser", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    // Flush all data queued in the content script because we will need that
+    // state to properly duplicate the given tab.
+    TabState.flush(aTab.linkedBrowser);
+
+    // Duplicate the tab state
+    let tabState = TabState.clone(aTab);
+
+    tabState.index += aDelta;
+    tabState.index = Math.max(1, Math.min(tabState.index, tabState.entries.length));
+    tabState.pinned = false;
+
+    this._setWindowStateBusy(aWindow);
+    let newTab = aTab == aWindow.gBrowser.selectedTab ?
+      aWindow.gBrowser.addTab(null, {relatedToCurrent: true, ownerTab: aTab}) :
+      aWindow.gBrowser.addTab();
+
+    this.restoreTabs(aWindow, [newTab], [tabState], 0,
+                     true /* Load this tab right away. */);
+
+    return newTab;
+  },
+
+  getClosedTabCount: function ssi_getClosedTabCount(aWindow) {
+    if ("__SSi" in aWindow) {
+      return this._windows[aWindow.__SSi]._closedTabs.length;
+    }
+
+    if (!DyingWindowCache.has(aWindow)) {
+      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    return DyingWindowCache.get(aWindow)._closedTabs.length;
+  },
+
+  getClosedTabData: function ssi_getClosedTabDataAt(aWindow) {
+    if ("__SSi" in aWindow) {
+      return this._toJSONString(this._windows[aWindow.__SSi]._closedTabs);
+    }
+
+    if (!DyingWindowCache.has(aWindow)) {
+      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    let data = DyingWindowCache.get(aWindow);
+    return this._toJSONString(data._closedTabs);
+  },
+
+  undoCloseTab: function ssi_undoCloseTab(aWindow, aIndex) {
+    if (!aWindow.__SSi) {
+      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    var closedTabs = this._windows[aWindow.__SSi]._closedTabs;
+
+    // default to the most-recently closed tab
+    aIndex = aIndex || 0;
+    if (!(aIndex in closedTabs)) {
+      throw Components.Exception("Invalid index: not in the closed tabs", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    // fetch the data of closed tab, while removing it from the array
+    let closedTab = closedTabs.splice(aIndex, 1).shift();
+    let closedTabState = closedTab.state;
+
+    this._setWindowStateBusy(aWindow);
+    // create a new tab
+    let tabbrowser = aWindow.gBrowser;
+    let tab = tabbrowser.addTab();
+
+    // restore tab content
+    this.restoreTabs(aWindow, [tab], [closedTabState], 1);
+
+    // restore the tab's position
+    tabbrowser.moveTabTo(tab, closedTab.pos);
+
+    // focus the tab's content area (bug 342432)
+    tab.linkedBrowser.focus();
+
+    return tab;
+  },
+
+  forgetClosedTab: function ssi_forgetClosedTab(aWindow, aIndex) {
+    if (!aWindow.__SSi) {
+      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    var closedTabs = this._windows[aWindow.__SSi]._closedTabs;
+
+    // default to the most-recently closed tab
+    aIndex = aIndex || 0;
+    if (!(aIndex in closedTabs)) {
+      throw Components.Exception("Invalid index: not in the closed tabs", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    // remove closed tab from the array
+    closedTabs.splice(aIndex, 1);
+  },
+
+  getClosedWindowCount: function ssi_getClosedWindowCount() {
+    return this._closedWindows.length;
+  },
+
+  getClosedWindowData: function ssi_getClosedWindowData() {
+    return this._toJSONString(this._closedWindows);
+  },
+
+  undoCloseWindow: function ssi_undoCloseWindow(aIndex) {
+    if (!(aIndex in this._closedWindows)) {
+      throw Components.Exception("Invalid index: not in the closed windows", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    // reopen the window
+    let state = { windows: this._closedWindows.splice(aIndex, 1) };
+    let window = this._openWindowWithState(state);
+    this.windowToFocus = window;
+    return window;
+  },
+
+  forgetClosedWindow: function ssi_forgetClosedWindow(aIndex) {
+    // default to the most-recently closed window
+    aIndex = aIndex || 0;
+    if (!(aIndex in this._closedWindows)) {
+      throw Components.Exception("Invalid index: not in the closed windows", Cr.NS_ERROR_INVALID_ARG);
+    }
+
+    // remove closed window from the array
+    this._closedWindows.splice(aIndex, 1);
+  },
+
+  getWindowValue: function ssi_getWindowValue(aWindow, aKey) {
+    if ("__SSi" in aWindow) {
+      var data = this._windows[aWindow.__SSi].extData || {};
+      return data[aKey] || "";
+    }
+
+    if (DyingWindowCache.has(aWindow)) {
+      let data = DyingWindowCache.get(aWindow).extData || {};
+      return data[aKey] || "";
+    }
+
+    throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
+  },
+
+  setWindowValue: function ssi_setWindowValue(aWindow, aKey, aStringValue) {
+    if (typeof aStringValue != "string") {
+      throw new TypeError("setWindowValue only accepts string values");
+    }
+
+    if (!("__SSi" in aWindow)) {
+      throw Components.Exception("Window is not tracked", Cr.NS_ERROR_INVALID_ARG);
+    }
+    if (!this._windows[aWindow.__SSi].extData) {
+      this._windows[aWindow.__SSi].extData = {};
+    }
+    this._windows[aWindow.__SSi].extData[aKey] = aStringValue;
+    this.saveStateDelayed(aWindow);
+  },
+
+  deleteWindowValue: function ssi_deleteWindowValue(aWindow, aKey) {
+    if (aWindow.__SSi && this._windows[aWindow.__SSi].extData &&
+        this._windows[aWindow.__SSi].extData[aKey])
+      delete this._windows[aWindow.__SSi].extData[aKey];
+    this.saveStateDelayed(aWindow);
+  },
+
+  getTabValue: function ssi_getTabValue(aTab, aKey) {
+    let data = {};
+    if (aTab.__SS_extdata) {
+      data = aTab.__SS_extdata;
+    }
+    else if (aTab.linkedBrowser.__SS_data && aTab.linkedBrowser.__SS_data.extData) {
+      // If the tab hasn't been fully restored, get the data from the to-be-restored data
+      data = aTab.linkedBrowser.__SS_data.extData;
+    }
+    return data[aKey] || "";
+  },
+
+  setTabValue: function ssi_setTabValue(aTab, aKey, aStringValue) {
+    if (typeof aStringValue != "string") {
+      throw new TypeError("setTabValue only accepts string values");
+    }
+
+    // If the tab hasn't been restored, then set the data there, otherwise we
+    // could lose newly added data.
+    let saveTo;
+    if (aTab.__SS_extdata) {
+      saveTo = aTab.__SS_extdata;
+    }
+    else if (aTab.linkedBrowser.__SS_data && aTab.linkedBrowser.__SS_data.extData) {
+      saveTo = aTab.linkedBrowser.__SS_data.extData;
+    }
+    else {
+      aTab.__SS_extdata = {};
+      saveTo = aTab.__SS_extdata;
+    }
+
+    saveTo[aKey] = aStringValue;
+    this.saveStateDelayed(aTab.ownerDocument.defaultView);
+  },
+
+  deleteTabValue: function ssi_deleteTabValue(aTab, aKey) {
+    // We want to make sure that if data is accessed early, we attempt to delete
+    // that data from __SS_data as well. Otherwise we'll throw in cases where
+    // data can be set or read.
+    let deleteFrom;
+    if (aTab.__SS_extdata) {
+      deleteFrom = aTab.__SS_extdata;
+    }
+    else if (aTab.linkedBrowser.__SS_data && aTab.linkedBrowser.__SS_data.extData) {
+      deleteFrom = aTab.linkedBrowser.__SS_data.extData;
+    }
+
+    if (deleteFrom && aKey in deleteFrom) {
+      delete deleteFrom[aKey];
+      this.saveStateDelayed(aTab.ownerDocument.defaultView);
+    }
+  },
+
+  getGlobalValue: function ssi_getGlobalValue(aKey) {
+    return this._globalState.get(aKey);
+  },
+
+  setGlobalValue: function ssi_setGlobalValue(aKey, aStringValue) {
+    if (typeof aStringValue != "string") {
+      throw new TypeError("setGlobalValue only accepts string values");
+    }
+
+    this._globalState.set(aKey, aStringValue);
+    this.saveStateDelayed();
+  },
+
+  deleteGlobalValue: function ssi_deleteGlobalValue(aKey) {
+    this._globalState.delete(aKey);
+    this.saveStateDelayed();
+  },
+
+  persistTabAttribute: function ssi_persistTabAttribute(aName) {
+    if (TabAttributes.persist(aName)) {
+      this.saveStateDelayed();
+    }
+  },
+
+  /**
+   * Restores the session state stored in LastSession. This will attempt
+   * to merge data into the current session. If a window was opened at startup
+   * with pinned tab(s), then the remaining data from the previous session for
+   * that window will be opened into that winddow. Otherwise new windows will
+   * be opened.
+   */
+  restoreLastSession: function ssi_restoreLastSession() {
+    // Use the public getter since it also checks PB mode
+    if (!this.canRestoreLastSession) {
+      throw Components.Exception("Last session can not be restored");
+    }
+
+    // First collect each window with its id...
+    let windows = {};
+    this._forEachBrowserWindow(function(aWindow) {
+      if (aWindow.__SS_lastSessionWindowID)
+        windows[aWindow.__SS_lastSessionWindowID] = aWindow;
+    });
+
+    let lastSessionState = LastSession.getState();
+
+    // This shouldn't ever be the case...
+    if (!lastSessionState.windows.length) {
+      throw Components.Exception("lastSessionState has no windows", Cr.NS_ERROR_UNEXPECTED);
+    }
+
+    // We're technically doing a restore, so set things up so we send the
+    // notification when we're done. We want to send "sessionstore-browser-state-restored".
+    this._restoreCount = lastSessionState.windows.length;
+    this._browserSetState = true;
+
+    // We want to re-use the last opened window instead of opening a new one in
+    // the case where it's "empty" and not associated with a window in the session.
+    // We will do more processing via _prepWindowToRestoreInto if we need to use
+    // the lastWindow.
+    let lastWindow = this._getMostRecentBrowserWindow();
+    let canUseLastWindow = lastWindow &&
+                           !lastWindow.__SS_lastSessionWindowID;
+
+    // global data must be restored before restoreWindow is called so that
+    // it happens before observers are notified
+    this._globalState.setFromState(lastSessionState);
+
+    // Restore into windows or open new ones as needed.
+    for (let i = 0; i < lastSessionState.windows.length; i++) {
+      let winState = lastSessionState.windows[i];
+      let lastSessionWindowID = winState.__lastSessionWindowID;
+      // delete lastSessionWindowID so we don't add that to the window again
+      delete winState.__lastSessionWindowID;
+
+      // See if we can use an open window. First try one that is associated with
+      // the state we're trying to restore and then fallback to the last selected
+      // window.
+      let windowToUse = windows[lastSessionWindowID];
+      if (!windowToUse && canUseLastWindow) {
+        windowToUse = lastWindow;
+        canUseLastWindow = false;
+      }
+
+      let [canUseWindow, canOverwriteTabs] = this._prepWindowToRestoreInto(windowToUse);
+
+      // If there's a window already open that we can restore into, use that
+      if (canUseWindow) {
+        // Since we're not overwriting existing tabs, we want to merge _closedTabs,
+        // putting existing ones first. Then make sure we're respecting the max pref.
+        if (winState._closedTabs && winState._closedTabs.length) {
+          let curWinState = this._windows[windowToUse.__SSi];
+          curWinState._closedTabs = curWinState._closedTabs.concat(winState._closedTabs);
+          curWinState._closedTabs.splice(this._max_tabs_undo, curWinState._closedTabs.length);
+        }
+
+        // Restore into that window - pretend it's a followup since we'll already
+        // have a focused window.
+        //XXXzpao This is going to merge extData together (taking what was in
+        //        winState over what is in the window already. The hack we have
+        //        in _preWindowToRestoreInto will prevent most (all?) Panorama
+        //        weirdness but we will still merge other extData.
+        //        Bug 588217 should make this go away by merging the group data.
+        let options = {overwriteTabs: canOverwriteTabs, isFollowUp: true};
+        this.restoreWindow(windowToUse, { windows: [winState] }, options);
+      }
+      else {
+        this._openWindowWithState({ windows: [winState] });
+      }
+    }
+
+    // Merge closed windows from this session with ones from last session
+    if (lastSessionState._closedWindows) {
+      this._closedWindows = this._closedWindows.concat(lastSessionState._closedWindows);
+      this._capClosedWindows();
+    }
+
+    if (lastSessionState.scratchpads) {
+      ScratchpadManager.restoreSession(lastSessionState.scratchpads);
+    }
+
+    // Set data that persists between sessions
+    this._recentCrashes = lastSessionState.session &&
+                          lastSessionState.session.recentCrashes || 0;
+
+    // Update the session start time using the restored session state.
+    this._updateSessionStartTime(lastSessionState);
+
+    LastSession.clear();
+  },
+
+  /**
+   * See if aWindow is usable for use when restoring a previous session via
+   * restoreLastSession. If usable, prepare it for use.
+   *
+   * @param aWindow
+   *        the window to inspect & prepare
+   * @returns [canUseWindow, canOverwriteTabs]
+   *          canUseWindow: can the window be used to restore into
+   *          canOverwriteTabs: all of the current tabs are home pages and we
+   *                            can overwrite them
+   */
+  _prepWindowToRestoreInto: function ssi_prepWindowToRestoreInto(aWindow) {
+    if (!aWindow)
+      return [false, false];
+
+    // We might be able to overwrite the existing tabs instead of just adding
+    // the previous session's tabs to the end. This will be set if possible.
+    let canOverwriteTabs = false;
+
+    // Step 1 of processing:
+    // Inspect extData for Panorama identifiers. If found, then we want to
+    // inspect further. If there is a single group, then we can use this
+    // window. If there are multiple groups then we won't use this window.
+    let groupsData = this.getWindowValue(aWindow, "tabview-groups");
+    if (groupsData) {
+      groupsData = JSON.parse(groupsData);
+
+      // If there are multiple groups, we don't want to use this window.
+      if (groupsData.totalNumber > 1)
+        return [false, false];
+    }
+
+    // Step 2 of processing:
+    // If we're still here, then the window is usable. Look at the open tabs in
+    // comparison to home pages. If all the tabs are home pages then we'll end
+    // up overwriting all of them. Otherwise we'll just close the tabs that
+    // match home pages. Tabs with the about:blank URI will always be
+    // overwritten.
+    let homePages = ["about:blank"];
+    let removableTabs = [];
+    let tabbrowser = aWindow.gBrowser;
+    let normalTabsLen = tabbrowser.tabs.length - tabbrowser._numPinnedTabs;
+    let startupPref = this._prefBranch.getIntPref("startup.page");
+    if (startupPref == 1)
+      homePages = homePages.concat(aWindow.gHomeButton.getHomePage().split("|"));
+
+    for (let i = tabbrowser._numPinnedTabs; i < tabbrowser.tabs.length; i++) {
+      let tab = tabbrowser.tabs[i];
+      if (homePages.indexOf(tab.linkedBrowser.currentURI.spec) != -1) {
+        removableTabs.push(tab);
+      }
+    }
+
+    if (tabbrowser.tabs.length == removableTabs.length) {
+      canOverwriteTabs = true;
+    }
+    else {
+      // If we're not overwriting all of the tabs, then close the home tabs.
+      for (let i = removableTabs.length - 1; i >= 0; i--) {
+        tabbrowser.removeTab(removableTabs.pop(), { animate: false });
+      }
+    }
+
+    return [true, canOverwriteTabs];
+  },
+
+  /* ........ Saving Functionality .............. */
+
+  /**
+   * Store window dimensions, visibility, sidebar
+   * @param aWindow
+   *        Window reference
+   */
+  _updateWindowFeatures: function ssi_updateWindowFeatures(aWindow) {
+    var winData = this._windows[aWindow.__SSi];
+
+    WINDOW_ATTRIBUTES.forEach(function(aAttr) {
+      winData[aAttr] = this._getWindowDimension(aWindow, aAttr);
+    }, this);
+
+    var hidden = WINDOW_HIDEABLE_FEATURES.filter(function(aItem) {
+      return aWindow[aItem] && !aWindow[aItem].visible;
+    });
+    if (hidden.length != 0)
+      winData.hidden = hidden.join(",");
+    else if (winData.hidden)
+      delete winData.hidden;
+
+    var sidebar = aWindow.document.getElementById("sidebar-box").getAttribute("sidebarcommand");
+    if (sidebar)
+      winData.sidebar = sidebar;
+    else if (winData.sidebar)
+      delete winData.sidebar;
+  },
+
+  /**
+   * gather session data as object
+   * @param aUpdateAll
+   *        Bool update all windows
+   * @returns object
+   */
+  getCurrentState: function (aUpdateAll) {
+    this._handleClosedWindows();
+
+    var activeWindow = this._getMostRecentBrowserWindow();
+
+    TelemetryStopwatch.start("FX_SESSION_RESTORE_COLLECT_ALL_WINDOWS_DATA_MS");
+    if (this._loadState == STATE_RUNNING) {
+      // update the data for all windows with activities since the last save operation
+      this._forEachBrowserWindow(function(aWindow) {
+        if (!this._isWindowLoaded(aWindow)) // window data is still in _statesToRestore
+          return;
+        if (aUpdateAll || DirtyWindows.has(aWindow) || aWindow == activeWindow) {
+          this._collectWindowData(aWindow);
+        }
+        else { // always update the window features (whose change alone never triggers a save operation)
+          this._updateWindowFeatures(aWindow);
+        }
+      });
+      DirtyWindows.clear();
+    }
+    TelemetryStopwatch.finish("FX_SESSION_RESTORE_COLLECT_ALL_WINDOWS_DATA_MS");
+
+    // An array that at the end will hold all current window data.
+    var total = [];
+    // The ids of all windows contained in 'total' in the same order.
+    var ids = [];
+    // The number of window that are _not_ popups.
+    var nonPopupCount = 0;
+    var ix;
+
+    // collect the data for all windows
+    for (ix in this._windows) {
+      if (this._windows[ix]._restoring) // window data is still in _statesToRestore
+        continue;
+      total.push(this._windows[ix]);
+      ids.push(ix);
+      if (!this._windows[ix].isPopup)
+        nonPopupCount++;
+    }
+
+    TelemetryStopwatch.start("FX_SESSION_RESTORE_COLLECT_COOKIES_MS");
+    SessionCookies.update(total);
+    TelemetryStopwatch.finish("FX_SESSION_RESTORE_COLLECT_COOKIES_MS");
+
+    // collect the data for all windows yet to be restored
+    for (ix in this._statesToRestore) {
+      for each (let winData in this._statesToRestore[ix].windows) {
+        total.push(winData);
+        if (!winData.isPopup)
+          nonPopupCount++;
+      }
+    }
+
+    // shallow copy this._closedWindows to preserve current state
+    let lastClosedWindowsCopy = this._closedWindows.slice();
+
+#ifndef XP_MACOSX
+    // If no non-popup browser window remains open, return the state of the last
+    // closed window(s). We only want to do this when we're actually "ending"
+    // the session.
+    //XXXzpao We should do this for _restoreLastWindow == true, but that has
+    //        its own check for popups. c.f. bug 597619
+    if (nonPopupCount == 0 && lastClosedWindowsCopy.length > 0 &&
+        this._loadState == STATE_QUITTING) {
+      // prepend the last non-popup browser window, so that if the user loads more tabs
+      // at startup we don't accidentally add them to a popup window
+      do {
+        total.unshift(lastClosedWindowsCopy.shift())
+      } while (total[0].isPopup && lastClosedWindowsCopy.length > 0)
+    }
+#endif
+
+    if (activeWindow) {
+      this.activeWindowSSiCache = activeWindow.__SSi || "";
+    }
+    ix = ids.indexOf(this.activeWindowSSiCache);
+    // We don't want to restore focus to a minimized window or a window which had all its
+    // tabs stripped out (doesn't exist).
+    if (ix != -1 && total[ix] && total[ix].sizemode == "minimized")
+      ix = -1;
+
+    let session = {
+      lastUpdate: Date.now(),
+      startTime: this._sessionStartTime,
+      recentCrashes: this._recentCrashes
+    };
+
+    // get open Scratchpad window states too
+    let scratchpads = ScratchpadManager.getSessionState();
+
+    let state = {
+      windows: total,
+      selectedWindow: ix + 1,
+      _closedWindows: lastClosedWindowsCopy,
+      session: session,
+      scratchpads: scratchpads,
+      global: this._globalState.getState()
+    };
+
+    // Persist the last session if we deferred restoring it
+    if (LastSession.canRestore) {
+      state.lastSessionState = LastSession.getState();
+    }
+
+    // If we were called by the SessionSaver and started with only a private
+    // window we want to pass the deferred initial state to not lose the
+    // previous session.
+    if (this._deferredInitialState) {
+      state.deferredInitialState = this._deferredInitialState;
+    }
+
+    return state;
+  },
+
+  /**
+   * serialize session data for a window
+   * @param aWindow
+   *        Window reference
+   * @returns string
+   */
+  _getWindowState: function ssi_getWindowState(aWindow) {
+    if (!this._isWindowLoaded(aWindow))
+      return this._statesToRestore[aWindow.__SS_restoreID];
+
+    if (this._loadState == STATE_RUNNING) {
+      this._collectWindowData(aWindow);
+    }
+
+    let windows = [this._windows[aWindow.__SSi]];
+    SessionCookies.update(windows);
+
+    return { windows: windows };
+  },
+
+  _collectWindowData: function ssi_collectWindowData(aWindow) {
+    if (!this._isWindowLoaded(aWindow))
+      return;
+    TelemetryStopwatch.start("FX_SESSION_RESTORE_COLLECT_SINGLE_WINDOW_DATA_MS");
+
+    let tabbrowser = aWindow.gBrowser;
+    let tabs = tabbrowser.tabs;
+    let winData = this._windows[aWindow.__SSi];
+    let tabsData = winData.tabs = [];
+
+    // update the internal state data for this window
+    for (let tab of tabs) {
+      tabsData.push(TabState.collect(tab));
+    }
+    winData.selected = tabbrowser.mTabBox.selectedIndex + 1;
+
+    this._updateWindowFeatures(aWindow);
+
+    // Make sure we keep __SS_lastSessionWindowID around for cases like entering
+    // or leaving PB mode.
+    if (aWindow.__SS_lastSessionWindowID)
+      this._windows[aWindow.__SSi].__lastSessionWindowID =
+        aWindow.__SS_lastSessionWindowID;
+
+    DirtyWindows.remove(aWindow);
+    TelemetryStopwatch.finish("FX_SESSION_RESTORE_COLLECT_SINGLE_WINDOW_DATA_MS");
+  },
+
+  /* ........ Restoring Functionality .............. */
+
+  /**
+   * restore features to a single window
+   * @param aWindow
+   *        Window reference
+   * @param aState
+   *        JS object or its eval'able source
+   * @param aOptions
+   *        {overwriteTabs: true} to overwrite existing tabs w/ new ones
+   *        {isFollowUp: true} if this is not the restoration of the 1st window
+   *        {firstWindow: true} if this is the first non-private window we're
+   *                            restoring in this session, that might open an
+   *                            external link as well
+   */
+  restoreWindow: function ssi_restoreWindow(aWindow, aState, aOptions = {}) {
+    let overwriteTabs = aOptions && aOptions.overwriteTabs;
+    let isFollowUp = aOptions && aOptions.isFollowUp;
+    let firstWindow = aOptions && aOptions.firstWindow;
+
+    if (isFollowUp) {
+      this.windowToFocus = aWindow;
+    }
+    // initialize window if necessary
+    if (aWindow && (!aWindow.__SSi || !this._windows[aWindow.__SSi]))
+      this.onLoad(aWindow);
+
+    try {
+      var root = typeof aState == "string" ? JSON.parse(aState) : aState;
+      if (!root.windows[0]) {
+        this._sendRestoreCompletedNotifications();
+        return; // nothing to restore
+      }
+    }
+    catch (ex) { // invalid state object - don't restore anything
+      debug(ex);
+      this._sendRestoreCompletedNotifications();
+      return;
+    }
+
+    TelemetryStopwatch.start("FX_SESSION_RESTORE_RESTORE_WINDOW_MS");
+
+    // We're not returning from this before we end up calling restoreTabs
+    // for this window, so make sure we send the SSWindowStateBusy event.
+    this._setWindowStateBusy(aWindow);
+
+    if (root._closedWindows)
+      this._closedWindows = root._closedWindows;
+
+    var winData;
+    if (!root.selectedWindow || root.selectedWindow > root.windows.length) {
+      root.selectedWindow = 0;
+    }
+
+    // open new windows for all further window entries of a multi-window session
+    // (unless they don't contain any tab data)
+    for (var w = 1; w < root.windows.length; w++) {
+      winData = root.windows[w];
+      if (winData && winData.tabs && winData.tabs[0]) {
+        var window = this._openWindowWithState({ windows: [winData] });
+        if (w == root.selectedWindow - 1) {
+          this.windowToFocus = window;
+        }
+      }
+    }
+    winData = root.windows[0];
+    if (!winData.tabs) {
+      winData.tabs = [];
+    }
+    // don't restore a single blank tab when we've had an external
+    // URL passed in for loading at startup (cf. bug 357419)
+    else if (firstWindow && !overwriteTabs && winData.tabs.length == 1 &&
+             (!winData.tabs[0].entries || winData.tabs[0].entries.length == 0)) {
+      winData.tabs = [];
+    }
+
+    var tabbrowser = aWindow.gBrowser;
+    var openTabCount = overwriteTabs ? tabbrowser.browsers.length : -1;
+    var newTabCount = winData.tabs.length;
+    var tabs = [];
+
+    // disable smooth scrolling while adding, moving, removing and selecting tabs
+    var tabstrip = tabbrowser.tabContainer.mTabstrip;
+    var smoothScroll = tabstrip.smoothScroll;
+    tabstrip.smoothScroll = false;
+
+    // unpin all tabs to ensure they are not reordered in the next loop
+    if (overwriteTabs) {
+      for (let t = tabbrowser._numPinnedTabs - 1; t > -1; t--)
+        tabbrowser.unpinTab(tabbrowser.tabs[t]);
+    }
+
+    // We need to keep track of the initially open tabs so that they
+    // can be moved to the end of the restored tabs.
+    let initialTabs = [];
+    if (!overwriteTabs && firstWindow) {
+      initialTabs = Array.slice(tabbrowser.tabs);
+    }
+
+    // make sure that the selected tab won't be closed in order to
+    // prevent unnecessary flickering
+    if (overwriteTabs && tabbrowser.selectedTab._tPos >= newTabCount)
+      tabbrowser.moveTabTo(tabbrowser.selectedTab, newTabCount - 1);
+
+    let numVisibleTabs = 0;
+
+    for (var t = 0; t < newTabCount; t++) {
+      tabs.push(t < openTabCount ?
+                tabbrowser.tabs[t] :
+                tabbrowser.addTab("about:blank", {skipAnimation: true}));
+
+      if (winData.tabs[t].pinned)
+        tabbrowser.pinTab(tabs[t]);
+
+      if (winData.tabs[t].hidden) {
+        tabbrowser.hideTab(tabs[t]);
+      }
+      else {
+        tabbrowser.showTab(tabs[t]);
+        numVisibleTabs++;
+      }
+    }
+
+    if (!overwriteTabs && firstWindow) {
+      // Move the originally open tabs to the end
+      let endPosition = tabbrowser.tabs.length - 1;
+      for (let i = 0; i < initialTabs.length; i++) {
+        tabbrowser.moveTabTo(initialTabs[i], endPosition);
+      }
+    }
+
+    // if all tabs to be restored are hidden, make the first one visible
+    if (!numVisibleTabs && winData.tabs.length) {
+      winData.tabs[0].hidden = false;
+      tabbrowser.showTab(tabs[0]);
+    }
+
+    // If overwriting tabs, we want to reset each tab's "restoring" state. Since
+    // we're overwriting those tabs, they should no longer be restoring. The
+    // tabs will be rebuilt and marked if they need to be restored after loading
+    // state (in restoreTabs).
+    if (overwriteTabs) {
+      for (let i = 0; i < tabbrowser.tabs.length; i++) {
+        let tab = tabbrowser.tabs[i];
+        if (tabbrowser.browsers[i].__SS_restoreState)
+          this._resetTabRestoringState(tab);
+      }
+    }
+
+    // We want to correlate the window with data from the last session, so
+    // assign another id if we have one. Otherwise clear so we don't do
+    // anything with it.
+    delete aWindow.__SS_lastSessionWindowID;
+    if (winData.__lastSessionWindowID)
+      aWindow.__SS_lastSessionWindowID = winData.__lastSessionWindowID;
+
+    // when overwriting tabs, remove all superflous ones
+    if (overwriteTabs && newTabCount < openTabCount) {
+      Array.slice(tabbrowser.tabs, newTabCount, openTabCount)
+           .forEach(tabbrowser.removeTab, tabbrowser);
+    }
+
+    if (overwriteTabs) {
+      this.restoreWindowFeatures(aWindow, winData);
+      delete this._windows[aWindow.__SSi].extData;
+    }
+    if (winData.cookies) {
+      this.restoreCookies(winData.cookies);
+    }
+    if (winData.extData) {
+      if (!this._windows[aWindow.__SSi].extData) {
+        this._windows[aWindow.__SSi].extData = {};
+      }
+      for (var key in winData.extData) {
+        this._windows[aWindow.__SSi].extData[key] = winData.extData[key];
+      }
+    }
+
+    let newClosedTabsData = winData._closedTabs || [];
+
+    if (overwriteTabs || firstWindow) {
+      // Overwrite existing closed tabs data when overwriteTabs=true
+      // or we're the first window to be restored.
+      this._windows[aWindow.__SSi]._closedTabs = newClosedTabsData;
+    } else if (this._max_tabs_undo > 0) {
+      // If we merge tabs, we also want to merge closed tabs data. We'll assume
+      // the restored tabs were closed more recently and append the current list
+      // of closed tabs to the new one...
+      newClosedTabsData =
+        newClosedTabsData.concat(this._windows[aWindow.__SSi]._closedTabs);
+
+      // ... and make sure that we don't exceed the max number of closed tabs
+      // we can restore.
+      this._windows[aWindow.__SSi]._closedTabs =
+        newClosedTabsData.slice(0, this._max_tabs_undo);
+    }
+
+    this.restoreTabs(aWindow, tabs, winData.tabs,
+      (overwriteTabs ? (parseInt(winData.selected || "1")) : 0));
+
+    if (aState.scratchpads) {
+      ScratchpadManager.restoreSession(aState.scratchpads);
+    }
+
+    // set smoothScroll back to the original value
+    tabstrip.smoothScroll = smoothScroll;
+
+    TelemetryStopwatch.finish("FX_SESSION_RESTORE_RESTORE_WINDOW_MS");
+
+    this._sendRestoreCompletedNotifications();
+  },
+
+  /**
+   * Sets the tabs restoring order with the following priority:
+   * Selected tab, pinned tabs, optimized visible tabs, other visible tabs and
+   * hidden tabs.
+   * @param aTabBrowser
+   *        Tab browser object
+   * @param aTabs
+   *        Array of tab references
+   * @param aTabData
+   *        Array of tab data
+   * @param aSelectedTab
+   *        Index of selected tab (1 is first tab, 0 no selected tab)
+   */
+  _setTabsRestoringOrder : function ssi__setTabsRestoringOrder(
+    aTabBrowser, aTabs, aTabData, aSelectedTab) {
+
+    // Store the selected tab. Need to substract one to get the index in aTabs.
+    let selectedTab;
+    if (aSelectedTab > 0 && aTabs[aSelectedTab - 1]) {
+      selectedTab = aTabs[aSelectedTab - 1];
+    }
+
+    // Store the pinned tabs and hidden tabs.
+    let pinnedTabs = [];
+    let pinnedTabsData = [];
+    let hiddenTabs = [];
+    let hiddenTabsData = [];
+    if (aTabs.length > 1) {
+      for (let t = aTabs.length - 1; t >= 0; t--) {
+        if (aTabData[t].pinned) {
+          pinnedTabs.unshift(aTabs.splice(t, 1)[0]);
+          pinnedTabsData.unshift(aTabData.splice(t, 1)[0]);
+        } else if (aTabData[t].hidden) {
+          hiddenTabs.unshift(aTabs.splice(t, 1)[0]);
+          hiddenTabsData.unshift(aTabData.splice(t, 1)[0]);
+        }
+      }
+    }
+
+    // Optimize the visible tabs only if there is a selected tab.
+    if (selectedTab) {
+      let selectedTabIndex = aTabs.indexOf(selectedTab);
+      if (selectedTabIndex > 0) {
+        let scrollSize = aTabBrowser.tabContainer.mTabstrip.scrollClientSize;
+        let tabWidth = aTabs[0].getBoundingClientRect().width;
+        let maxVisibleTabs = Math.ceil(scrollSize / tabWidth);
+        if (maxVisibleTabs < aTabs.length) {
+          let firstVisibleTab = 0;
+          let nonVisibleTabsCount = aTabs.length - maxVisibleTabs;
+          if (nonVisibleTabsCount >= selectedTabIndex) {
+            // Selected tab is leftmost since we scroll to it when possible.
+            firstVisibleTab = selectedTabIndex;
+          } else {
+            // Selected tab is rightmost or no more room to scroll right.
+            firstVisibleTab = nonVisibleTabsCount;
+          }
+          aTabs = aTabs.splice(firstVisibleTab, maxVisibleTabs).concat(aTabs);
+          aTabData =
+            aTabData.splice(firstVisibleTab, maxVisibleTabs).concat(aTabData);
+        }
+      }
+    }
+
+    // Merge the stored tabs in order.
+    aTabs = pinnedTabs.concat(aTabs, hiddenTabs);
+    aTabData = pinnedTabsData.concat(aTabData, hiddenTabsData);
+
+    // Load the selected tab to the first position and select it.
+    if (selectedTab) {
+      let selectedTabIndex = aTabs.indexOf(selectedTab);
+      if (selectedTabIndex > 0) {
+        aTabs = aTabs.splice(selectedTabIndex, 1).concat(aTabs);
+        aTabData = aTabData.splice(selectedTabIndex, 1).concat(aTabData);
+      }
+      aTabBrowser.selectedTab = selectedTab;
+    }
+
+    return [aTabs, aTabData];
+  },
+
+  /**
+   * Manage history restoration for a window
+   * @param aWindow
+   *        Window to restore the tabs into
+   * @param aTabs
+   *        Array of tab references
+   * @param aTabData
+   *        Array of tab data
+   * @param aSelectTab
+   *        Index of selected tab
+   * @param aRestoreImmediately
+   *        Flag to indicate whether the given set of tabs aTabs should be
+   *        restored/loaded immediately even if restore_on_demand = true
+   */
+  restoreTabs: function (aWindow, aTabs, aTabData, aSelectTab,
+                         aRestoreImmediately = false)
+  {
+
+    var tabbrowser = aWindow.gBrowser;
+
+    if (!this._isWindowLoaded(aWindow)) {
+      // from now on, the data will come from the actual window
+      delete this._statesToRestore[aWindow.__SS_restoreID];
+      delete aWindow.__SS_restoreID;
+      delete this._windows[aWindow.__SSi]._restoring;
+    }
+
+    // It's important to set the window state to dirty so that
+    // we collect their data for the first time when saving state.
+    DirtyWindows.add(aWindow);
+
+    // Set the state to restore as the window's current state. Normally, this
+    // will just be overridden the next time we collect state but we need this
+    // as a fallback should Firefox be shutdown early without notifying us
+    // beforehand.
+    this._windows[aWindow.__SSi].tabs = aTabData.slice();
+    this._windows[aWindow.__SSi].selected = aSelectTab;
+
+    if (aTabs.length == 0) {
+      // This is normally done later, but as we're returning early
+      // here we need to take care of it.
+      this._setWindowStateReady(aWindow);
+      return;
+    }
+
+    // Sets the tabs restoring order.
+    [aTabs, aTabData] =
+      this._setTabsRestoringOrder(tabbrowser, aTabs, aTabData, aSelectTab);
+
+    // Prepare the tabs so that they can be properly restored. We'll pin/unpin
+    // and show/hide tabs as necessary. We'll also set the labels, user typed
+    // value, and attach a copy of the tab's data in case we close it before
+    // it's been restored.
+    for (let t = 0; t < aTabs.length; t++) {
+      let tab = aTabs[t];
+      let browser = tabbrowser.getBrowserForTab(tab);
+      let tabData = aTabData[t];
+
+      if (tabData.pinned)
+        tabbrowser.pinTab(tab);
+      else
+        tabbrowser.unpinTab(tab);
+
+      if (tabData.hidden)
+        tabbrowser.hideTab(tab);
+      else
+        tabbrowser.showTab(tab);
+
+      if (tabData.lastAccessed) {
+        tab.lastAccessed = tabData.lastAccessed;
+      }
+
+      if ("attributes" in tabData) {
+        // Ensure that we persist tab attributes restored from previous sessions.
+        Object.keys(tabData.attributes).forEach(a => TabAttributes.persist(a));
+      }
+
+      if (!tabData.entries) {
+        tabData.entries = [];
+      }
+      if (tabData.extData) {
+        tab.__SS_extdata = {};
+        for (let key in tabData.extData)
+         tab.__SS_extdata[key] = tabData.extData[key];
+      } else {
+        delete tab.__SS_extdata;
+      }
+
+      // Flush all data from the content script synchronously. This is done so
+      // that all async messages that are still on their way to chrome will
+      // be ignored and don't override any tab data set when restoring.
+      TabState.flush(tab.linkedBrowser);
+
+      // Ensure the index is in bounds.
+      let activeIndex = (tabData.index || tabData.entries.length) - 1;
+      activeIndex = Math.min(activeIndex, tabData.entries.length - 1);
+      activeIndex = Math.max(activeIndex, 0);
+
+      // Save the index in case we updated it above.
+      tabData.index = activeIndex + 1;
+
+      // In electrolysis, we may need to change the browser's remote
+      // attribute so that it runs in a content process.
+      let activePageData = tabData.entries[activeIndex] || null;
+      let uri = activePageData ? activePageData.url || null : null;
+      tabbrowser.updateBrowserRemoteness(browser, uri);
+
+      // Start a new epoch and include the epoch in the restoreHistory
+      // message. If a message is received that relates to a previous epoch, we
+      // discard it.
+      let epoch = this._nextRestoreEpoch++;
+      this._browserEpochs.set(browser.permanentKey, epoch);
+
+      // keep the data around to prevent dataloss in case
+      // a tab gets closed before it's been properly restored
+      browser.__SS_data = tabData;
+      browser.__SS_restoreState = TAB_STATE_NEEDS_RESTORE;
+      browser.setAttribute("pending", "true");
+      tab.setAttribute("pending", "true");
+
+      // Update the persistent tab state cache with |tabData| information.
+      TabStateCache.update(browser, {
+        history: {entries: tabData.entries, index: tabData.index},
+        scroll: tabData.scroll || null,
+        storage: tabData.storage || null,
+        formdata: tabData.formdata || null,
+        disallow: tabData.disallow || null,
+        pageStyle: tabData.pageStyle || null
+      });
+
+      browser.messageManager.sendAsyncMessage("SessionStore:restoreHistory",
+                                              {tabData: tabData, epoch: epoch});
+
+      // Restore tab attributes.
+      if ("attributes" in tabData) {
+        TabAttributes.set(tab, tabData.attributes);
+      }
+
+      // This could cause us to ignore MAX_CONCURRENT_TAB_RESTORES a bit, but
+      // it ensures each window will have its selected tab loaded.
+      if (aRestoreImmediately || tabbrowser.selectedBrowser == browser) {
+        this.restoreTabContent(tab);
+      } else {
+        TabRestoreQueue.add(tab);
+        this.restoreNextTab();
+      }
+    }
+
+    this._setWindowStateReady(aWindow);
+  },
+
+  /**
+   * Restores the specified tab. If the tab can't be restored (eg, no history or
+   * calling gotoIndex fails), then state changes will be rolled back.
+   * This method will check if gTabsProgressListener is attached to the tab's
+   * window, ensuring that we don't get caught without one.
+   * This method removes the session history listener right before starting to
+   * attempt a load. This will prevent cases of "stuck" listeners.
+   * If this method returns false, then it is up to the caller to decide what to
+   * do. In the common case (restoreNextTab), we will want to then attempt to
+   * restore the next tab. In the other case (selecting the tab, reloading the
+   * tab), the caller doesn't actually want to do anything if no page is loaded.
+   *
+   * @param aTab
+   *        the tab to restore
+   *
+   * @returns true/false indicating whether or not a load actually happened
+   */
+  restoreTabContent: function (aTab) {
+    let window = aTab.ownerDocument.defaultView;
+    let browser = aTab.linkedBrowser;
+    let tabData = browser.__SS_data;
+
+    // Make sure that this tab is removed from the priority queue.
+    TabRestoreQueue.remove(aTab);
+
+    // Increase our internal count.
+    this._tabsRestoringCount++;
+
+    // Set this tab's state to restoring
+    browser.__SS_restoreState = TAB_STATE_RESTORING;
+    browser.removeAttribute("pending");
+    aTab.removeAttribute("pending");
+
+    let activeIndex = tabData.index - 1;
+
+    // Attach data that will be restored on "load" event, after tab is restored.
+    if (tabData.entries.length) {
+      // restore those aspects of the currently active documents which are not
+      // preserved in the plain history entries (mainly scroll state and text data)
+      browser.__SS_restore_data = tabData.entries[activeIndex] || {};
+    } else {
+      browser.__SS_restore_data = {};
+    }
+
+    browser.__SS_restore_tab = aTab;
+
+    browser.messageManager.sendAsyncMessage("SessionStore:restoreTabContent");
+  },
+
+  /**
+   * This _attempts_ to restore the next available tab. If the restore fails,
+   * then we will attempt the next one.
+   * There are conditions where this won't do anything:
+   *   if we're in the process of quitting
+   *   if there are no tabs to restore
+   *   if we have already reached the limit for number of tabs to restore
+   */
+  restoreNextTab: function ssi_restoreNextTab() {
+    // If we call in here while quitting, we don't actually want to do anything
+    if (this._loadState == STATE_QUITTING)
+      return;
+
+    // Don't exceed the maximum number of concurrent tab restores.
+    if (this._tabsRestoringCount >= MAX_CONCURRENT_TAB_RESTORES)
+      return;
+
+    let tab = TabRestoreQueue.shift();
+    if (tab) {
+      this.restoreTabContent(tab);
+    }
+  },
+
+  /**
+   * Restore visibility and dimension features to a window
+   * @param aWindow
+   *        Window reference
+   * @param aWinData
+   *        Object containing session data for the window
+   */
+  restoreWindowFeatures: function ssi_restoreWindowFeatures(aWindow, aWinData) {
+    var hidden = (aWinData.hidden)?aWinData.hidden.split(","):[];
+    WINDOW_HIDEABLE_FEATURES.forEach(function(aItem) {
+      aWindow[aItem].visible = hidden.indexOf(aItem) == -1;
+    });
+
+    if (aWinData.isPopup) {
+      this._windows[aWindow.__SSi].isPopup = true;
+      if (aWindow.gURLBar) {
+        aWindow.gURLBar.readOnly = true;
+        aWindow.gURLBar.setAttribute("enablehistory", "false");
+      }
+    }
+    else {
+      delete this._windows[aWindow.__SSi].isPopup;
+      if (aWindow.gURLBar) {
+        aWindow.gURLBar.readOnly = false;
+        aWindow.gURLBar.setAttribute("enablehistory", "true");
+      }
+    }
+
+    var _this = this;
+    aWindow.setTimeout(function() {
+      _this.restoreDimensions.apply(_this, [aWindow,
+        +aWinData.width || 0,
+        +aWinData.height || 0,
+        "screenX" in aWinData ? +aWinData.screenX : NaN,
+        "screenY" in aWinData ? +aWinData.screenY : NaN,
+        aWinData.sizemode || "", aWinData.sidebar || ""]);
+    }, 0);
+  },
+
+  /**
+   * Restore a window's dimensions
+   * @param aWidth
+   *        Window width
+   * @param aHeight
+   *        Window height
+   * @param aLeft
+   *        Window left
+   * @param aTop
+   *        Window top
+   * @param aSizeMode
+   *        Window size mode (eg: maximized)
+   * @param aSidebar
+   *        Sidebar command
+   */
+  restoreDimensions: function ssi_restoreDimensions(aWindow, aWidth, aHeight, aLeft, aTop, aSizeMode, aSidebar) {
+    var win = aWindow;
+    var _this = this;
+    function win_(aName) { return _this._getWindowDimension(win, aName); }
+
+    // find available space on the screen where this window is being placed
+    let screen = gScreenManager.screenForRect(aLeft, aTop, aWidth, aHeight);
+    if (screen) {
+      let screenLeft = {}, screenTop = {}, screenWidth = {}, screenHeight = {};
+      screen.GetAvailRectDisplayPix(screenLeft, screenTop, screenWidth, screenHeight);
+      // constrain the dimensions to the actual space available
+      if (aWidth > screenWidth.value) {
+        aWidth = screenWidth.value;
+      }
+      if (aHeight > screenHeight.value) {
+        aHeight = screenHeight.value;
+      }
+      // and then pull the window within the screen's bounds
+      if (aLeft < screenLeft.value) {
+        aLeft = screenLeft.value;
+      } else if (aLeft + aWidth > screenLeft.value + screenWidth.value) {
+        aLeft = screenLeft.value + screenWidth.value - aWidth;
+      }
+      if (aTop < screenTop.value) {
+        aTop = screenTop.value;
+      } else if (aTop + aHeight > screenTop.value + screenHeight.value) {
+        aTop = screenTop.value + screenHeight.value - aHeight;
+      }
+    }
+
+    // only modify those aspects which aren't correct yet
+    if (aWidth && aHeight && (aWidth != win_("width") || aHeight != win_("height"))) {
+      // Don't resize the window if it's currently maximized and we would
+      // maximize it again shortly after.
+      if (aSizeMode != "maximized" || win_("sizemode") != "maximized") {
+        aWindow.resizeTo(aWidth, aHeight);
+      }
+    }
+    if (!isNaN(aLeft) && !isNaN(aTop) && (aLeft != win_("screenX") || aTop != win_("screenY"))) {
+      aWindow.moveTo(aLeft, aTop);
+    }
+    if (aSizeMode && win_("sizemode") != aSizeMode)
+    {
+      switch (aSizeMode)
+      {
+      case "maximized":
+        aWindow.maximize();
+        break;
+      case "minimized":
+        aWindow.minimize();
+        break;
+      case "normal":
+        aWindow.restore();
+        break;
+      }
+    }
+    var sidebar = aWindow.document.getElementById("sidebar-box");
+    if (sidebar.getAttribute("sidebarcommand") != aSidebar) {
+      aWindow.toggleSidebar(aSidebar);
+    }
+    // since resizing/moving a window brings it to the foreground,
+    // we might want to re-focus the last focused window
+    if (this.windowToFocus) {
+      this.windowToFocus.focus();
+    }
+  },
+
+  /**
+   * Restores cookies
+   * @param aCookies
+   *        Array of cookie objects
+   */
+  restoreCookies: function ssi_restoreCookies(aCookies) {
+    // MAX_EXPIRY should be 2^63-1, but JavaScript can't handle that precision
+    var MAX_EXPIRY = Math.pow(2, 62);
+    for (let i = 0; i < aCookies.length; i++) {
+      var cookie = aCookies[i];
+      try {
+        Services.cookies.add(cookie.host, cookie.path || "", cookie.name || "",
+                             cookie.value, !!cookie.secure, !!cookie.httponly, true,
+                             "expiry" in cookie ? cookie.expiry : MAX_EXPIRY);
+      }
+      catch (ex) { console.error(ex); } // don't let a single cookie stop recovering
+    }
+  },
+
+  /* ........ Disk Access .............. */
+
+  /**
+   * Save the current session state to disk, after a delay.
+   *
+   * @param aWindow (optional)
+   *        Will mark the given window as dirty so that we will recollect its
+   *        data before we start writing.
+   */
+  saveStateDelayed: function (aWindow = null) {
+    if (aWindow) {
+      DirtyWindows.add(aWindow);
+    }
+
+    SessionSaver.runDelayed();
+  },
+
+  /* ........ Auxiliary Functions .............. */
+
+  /**
+   * Update the session start time and send a telemetry measurement
+   * for the number of days elapsed since the session was started.
+   *
+   * @param state
+   *        The session state.
+   */
+  _updateSessionStartTime: function ssi_updateSessionStartTime(state) {
+    // Attempt to load the session start time from the session state
+    if (state.session && state.session.startTime) {
+      this._sessionStartTime = state.session.startTime;
+
+      // ms to days
+      let sessionLength = (Date.now() - this._sessionStartTime) / MS_PER_DAY;
+
+      if (sessionLength > 0) {
+        // Submit the session length telemetry measurement
+        Services.telemetry.getHistogramById("FX_SESSION_RESTORE_SESSION_LENGTH").add(sessionLength);
+      }
+    }
+  },
+
+  /**
+   * call a callback for all currently opened browser windows
+   * (might miss the most recent one)
+   * @param aFunc
+   *        Callback each window is passed to
+   */
+  _forEachBrowserWindow: function ssi_forEachBrowserWindow(aFunc) {
+    var windowsEnum = Services.wm.getEnumerator("navigator:browser");
+
+    while (windowsEnum.hasMoreElements()) {
+      var window = windowsEnum.getNext();
+      if (window.__SSi && !window.closed) {
+        aFunc.call(this, window);
+      }
+    }
+  },
+
+  /**
+   * Returns most recent window
+   * @returns Window reference
+   */
+  _getMostRecentBrowserWindow: function ssi_getMostRecentBrowserWindow() {
+    return RecentWindow.getMostRecentBrowserWindow({ allowPopups: true });
+  },
+
+  /**
+   * Calls onClose for windows that are determined to be closed but aren't
+   * destroyed yet, which would otherwise cause getBrowserState and
+   * setBrowserState to treat them as open windows.
+   */
+  _handleClosedWindows: function ssi_handleClosedWindows() {
+    var windowsEnum = Services.wm.getEnumerator("navigator:browser");
+
+    while (windowsEnum.hasMoreElements()) {
+      var window = windowsEnum.getNext();
+      if (window.closed) {
+        this.onClose(window);
+      }
+    }
+  },
+
+  /**
+   * open a new browser window for a given session state
+   * called when restoring a multi-window session
+   * @param aState
+   *        Object containing session data
+   */
+  _openWindowWithState: function ssi_openWindowWithState(aState) {
+    var argString = Cc["@mozilla.org/supports-string;1"].
+                    createInstance(Ci.nsISupportsString);
+    argString.data = "";
+
+    // Build feature string
+    let features = "chrome,dialog=no,macsuppressanimation,all";
+    let winState = aState.windows[0];
+    WINDOW_ATTRIBUTES.forEach(function(aFeature) {
+      // Use !isNaN as an easy way to ignore sizemode and check for numbers
+      if (aFeature in winState && !isNaN(winState[aFeature]))
+        features += "," + aFeature + "=" + winState[aFeature];
+    });
+
+    if (winState.isPrivate) {
+      features += ",private";
+    }
+
+    var window =
+      Services.ww.openWindow(null, this._prefBranch.getCharPref("chromeURL"),
+                             "_blank", features, argString);
+
+    do {
+      var ID = "window" + Math.random();
+    } while (ID in this._statesToRestore);
+    this._statesToRestore[(window.__SS_restoreID = ID)] = aState;
+
+    return window;
+  },
+
+  /**
+   * Gets the tab for the given browser. This should be marginally better
+   * than using tabbrowser's getTabForContentWindow. This assumes the browser
+   * is the linkedBrowser of a tab, not a dangling browser.
+   *
+   * @param aBrowser
+   *        The browser from which to get the tab.
+   */
+  _getTabForBrowser: function ssi_getTabForBrowser(aBrowser) {
+    let window = aBrowser.ownerDocument.defaultView;
+    for (let i = 0; i < window.gBrowser.tabs.length; i++) {
+      let tab = window.gBrowser.tabs[i];
+      if (tab.linkedBrowser == aBrowser)
+        return tab;
+    }
+    return undefined;
+  },
+
+  /**
+   * Whether or not to resume session, if not recovering from a crash.
+   * @returns bool
+   */
+  _doResumeSession: function ssi_doResumeSession() {
+    return this._prefBranch.getIntPref("startup.page") == 3 ||
+           this._prefBranch.getBoolPref("sessionstore.resume_session_once");
+  },
+
+  /**
+   * whether the user wants to load any other page at startup
+   * (except the homepage) - needed for determining whether to overwrite the current tabs
+   * C.f.: nsBrowserContentHandler's defaultArgs implementation.
+   * @returns bool
+   */
+  _isCmdLineEmpty: function ssi_isCmdLineEmpty(aWindow, aState) {
+    var pinnedOnly = aState.windows &&
+                     aState.windows.every(function (win)
+                       win.tabs.every(function (tab) tab.pinned));
+
+    let hasFirstArgument = aWindow.arguments && aWindow.arguments[0];
+    if (!pinnedOnly) {
+      let defaultArgs = Cc["@mozilla.org/browser/clh;1"].
+                        getService(Ci.nsIBrowserHandler).defaultArgs;
+      if (aWindow.arguments &&
+          aWindow.arguments[0] &&
+          aWindow.arguments[0] == defaultArgs)
+        hasFirstArgument = false;
+    }
+
+    return !hasFirstArgument;
+  },
+
+  /**
+   * on popup windows, the XULWindow's attributes seem not to be set correctly
+   * we use thus JSDOMWindow attributes for sizemode and normal window attributes
+   * (and hope for reasonable values when maximized/minimized - since then
+   * outerWidth/outerHeight aren't the dimensions of the restored window)
+   * @param aWindow
+   *        Window reference
+   * @param aAttribute
+   *        String sizemode | width | height | other window attribute
+   * @returns string
+   */
+  _getWindowDimension: function ssi_getWindowDimension(aWindow, aAttribute) {
+    if (aAttribute == "sizemode") {
+      switch (aWindow.windowState) {
+      case aWindow.STATE_FULLSCREEN:
+      case aWindow.STATE_MAXIMIZED:
+        return "maximized";
+      case aWindow.STATE_MINIMIZED:
+        return "minimized";
+      default:
+        return "normal";
+      }
+    }
+
+    var dimension;
+    switch (aAttribute) {
+    case "width":
+      dimension = aWindow.outerWidth;
+      break;
+    case "height":
+      dimension = aWindow.outerHeight;
+      break;
+    default:
+      dimension = aAttribute in aWindow ? aWindow[aAttribute] : "";
+      break;
+    }
+
+    if (aWindow.windowState == aWindow.STATE_NORMAL) {
+      return dimension;
+    }
+    return aWindow.document.documentElement.getAttribute(aAttribute) || dimension;
+  },
+
+  /**
+   * Get nsIURI from string
+   * @param string
+   * @returns nsIURI
+   */
+  _getURIFromString: function ssi_getURIFromString(aString) {
+    return Services.io.newURI(aString, null, null);
+  },
+
+  /**
+   * @param aState is a session state
+   * @param aRecentCrashes is the number of consecutive crashes
+   * @returns whether a restore page will be needed for the session state
+   */
+  _needsRestorePage: function ssi_needsRestorePage(aState, aRecentCrashes) {
+    const SIX_HOURS_IN_MS = 6 * 60 * 60 * 1000;
+
+    // don't display the page when there's nothing to restore
+    let winData = aState.windows || null;
+    if (!winData || winData.length == 0)
+      return false;
+
+    // don't wrap a single about:sessionrestore page
+    if (this._hasSingleTabWithURL(winData, "about:sessionrestore") ||
+        this._hasSingleTabWithURL(winData, "about:welcomeback")) {
+      return false;
+    }
+
+    // don't automatically restore in Safe Mode
+    if (Services.appinfo.inSafeMode)
+      return true;
+
+    let max_resumed_crashes =
+      this._prefBranch.getIntPref("sessionstore.max_resumed_crashes");
+    let sessionAge = aState.session && aState.session.lastUpdate &&
+                     (Date.now() - aState.session.lastUpdate);
+
+    return max_resumed_crashes != -1 &&
+           (aRecentCrashes > max_resumed_crashes ||
+            sessionAge && sessionAge >= SIX_HOURS_IN_MS);
+  },
+
+  /**
+   * @param aWinData is the set of windows in session state
+   * @param aURL is the single URL we're looking for
+   * @returns whether the window data contains only the single URL passed
+   */
+  _hasSingleTabWithURL: function(aWinData, aURL) {
+    if (aWinData &&
+        aWinData.length == 1 &&
+        aWinData[0].tabs &&
+        aWinData[0].tabs.length == 1 &&
+        aWinData[0].tabs[0].entries &&
+        aWinData[0].tabs[0].entries.length == 1) {
+      return aURL == aWinData[0].tabs[0].entries[0].url;
+    }
+    return false;
+  },
+
+  /**
+   * Determine if the tab state we're passed is something we should save. This
+   * is used when closing a tab or closing a window with a single tab
+   *
+   * @param aTabState
+   *        The current tab state
+   * @returns boolean
+   */
+  _shouldSaveTabState: function ssi_shouldSaveTabState(aTabState) {
+    // If the tab has only a transient about: history entry, no other
+    // session history, and no userTypedValue, then we don't actually want to
+    // store this tab's data.
+    return aTabState.entries.length &&
+           !(aTabState.entries.length == 1 &&
+                (aTabState.entries[0].url == "about:blank" ||
+                 aTabState.entries[0].url == "about:newtab") &&
+                 !aTabState.userTypedValue);
+  },
+
+  /**
+   * This is going to take a state as provided at startup (via
+   * nsISessionStartup.state) and split it into 2 parts. The first part
+   * (defaultState) will be a state that should still be restored at startup,
+   * while the second part (state) is a state that should be saved for later.
+   * defaultState will be comprised of windows with only pinned tabs, extracted
+   * from state. It will contain the cookies that go along with the history
+   * entries in those tabs. It will also contain window position information.
+   *
+   * defaultState will be restored at startup. state will be passed into
+   * LastSession and will be kept in case the user explicitly wants
+   * to restore the previous session (publicly exposed as restoreLastSession).
+   *
+   * @param state
+   *        The state, presumably from nsISessionStartup.state
+   * @returns [defaultState, state]
+   */
+  _prepDataForDeferredRestore: function ssi_prepDataForDeferredRestore(state) {
+    // Make sure that we don't modify the global state as provided by
+    // nsSessionStartup.state.
+    state = Cu.cloneInto(state, {});
+
+    let defaultState = { windows: [], selectedWindow: 1 };
+
+    state.selectedWindow = state.selectedWindow || 1;
+
+    // Look at each window, remove pinned tabs, adjust selectedindex,
+    // remove window if necessary.
+    for (let wIndex = 0; wIndex < state.windows.length;) {
+      let window = state.windows[wIndex];
+      window.selected = window.selected || 1;
+      // We're going to put the state of the window into this object
+      let pinnedWindowState = { tabs: [], cookies: []};
+      for (let tIndex = 0; tIndex < window.tabs.length;) {
+        if (window.tabs[tIndex].pinned) {
+          // Adjust window.selected
+          if (tIndex + 1 < window.selected)
+            window.selected -= 1;
+          else if (tIndex + 1 == window.selected)
+            pinnedWindowState.selected = pinnedWindowState.tabs.length + 2;
+            // + 2 because the tab isn't actually in the array yet
+
+          // Now add the pinned tab to our window
+          pinnedWindowState.tabs =
+            pinnedWindowState.tabs.concat(window.tabs.splice(tIndex, 1));
+          // We don't want to increment tIndex here.
+          continue;
+        }
+        tIndex++;
+      }
+
+      // At this point the window in the state object has been modified (or not)
+      // We want to build the rest of this new window object if we have pinnedTabs.
+      if (pinnedWindowState.tabs.length) {
+        // First get the other attributes off the window
+        WINDOW_ATTRIBUTES.forEach(function(attr) {
+          if (attr in window) {
+            pinnedWindowState[attr] = window[attr];
+            delete window[attr];
+          }
+        });
+        // We're just copying position data into the pinned window.
+        // Not copying over:
+        // - _closedTabs
+        // - extData
+        // - isPopup
+        // - hidden
+
+        // Assign a unique ID to correlate the window to be opened with the
+        // remaining data
+        window.__lastSessionWindowID = pinnedWindowState.__lastSessionWindowID
+                                     = "" + Date.now() + Math.random();
+
+        // Extract the cookies that belong with each pinned tab
+        this._splitCookiesFromWindow(window, pinnedWindowState);
+
+        // Actually add this window to our defaultState
+        defaultState.windows.push(pinnedWindowState);
+        // Remove the window from the state if it doesn't have any tabs
+        if (!window.tabs.length) {
+          if (wIndex + 1 <= state.selectedWindow)
+            state.selectedWindow -= 1;
+          else if (wIndex + 1 == state.selectedWindow)
+            defaultState.selectedIndex = defaultState.windows.length + 1;
+
+          state.windows.splice(wIndex, 1);
+          // We don't want to increment wIndex here.
+          continue;
+        }
+
+
+      }
+      wIndex++;
+    }
+
+    return [defaultState, state];
+  },
+
+  /**
+   * Splits out the cookies from aWinState into aTargetWinState based on the
+   * tabs that are in aTargetWinState.
+   * This alters the state of aWinState and aTargetWinState.
+   */
+  _splitCookiesFromWindow:
+    function ssi_splitCookiesFromWindow(aWinState, aTargetWinState) {
+    if (!aWinState.cookies || !aWinState.cookies.length)
+      return;
+
+    // Get the hosts for history entries in aTargetWinState
+    let cookieHosts = SessionCookies.getHostsForWindow(aTargetWinState);
+
+    // By creating a regex we reduce overhead and there is only one loop pass
+    // through either array (cookieHosts and aWinState.cookies).
+    let hosts = Object.keys(cookieHosts).join("|").replace("\\.", "\\.", "g");
+    // If we don't actually have any hosts, then we don't want to do anything.
+    if (!hosts.length)
+      return;
+    let cookieRegex = new RegExp(".*(" + hosts + ")");
+    for (let cIndex = 0; cIndex < aWinState.cookies.length;) {
+      if (cookieRegex.test(aWinState.cookies[cIndex].host)) {
+        aTargetWinState.cookies =
+          aTargetWinState.cookies.concat(aWinState.cookies.splice(cIndex, 1));
+        continue;
+      }
+      cIndex++;
+    }
+  },
+
+  /**
+   * Converts a JavaScript object into a JSON string
+   * (see http://www.json.org/ for more information).
+   *
+   * The inverse operation consists of JSON.parse(JSON_string).
+   *
+   * @param aJSObject is the object to be converted
+   * @returns the object's JSON representation
+   */
+  _toJSONString: function ssi_toJSONString(aJSObject) {
+    return JSON.stringify(aJSObject);
+  },
+
+  _sendRestoreCompletedNotifications: function ssi_sendRestoreCompletedNotifications() {
+    // not all windows restored, yet
+    if (this._restoreCount > 1) {
+      this._restoreCount--;
+      return;
+    }
+
+    // observers were already notified
+    if (this._restoreCount == -1)
+      return;
+
+    // This was the last window restored at startup, notify observers.
+    Services.obs.notifyObservers(null,
+      this._browserSetState ? NOTIFY_BROWSER_STATE_RESTORED : NOTIFY_WINDOWS_RESTORED,
+      "");
+
+    this._browserSetState = false;
+    this._restoreCount = -1;
+  },
+
+   /**
+   * Set the given window's busy state
+   * @param aWindow the window
+   * @param aValue the window's busy state
+   */
+  _setWindowStateBusyValue:
+    function ssi_changeWindowStateBusyValue(aWindow, aValue) {
+
+    this._windows[aWindow.__SSi].busy = aValue;
+
+    // Keep the to-be-restored state in sync because that is returned by
+    // getWindowState() as long as the window isn't loaded, yet.
+    if (!this._isWindowLoaded(aWindow)) {
+      let stateToRestore = this._statesToRestore[aWindow.__SS_restoreID].windows[0];
+      stateToRestore.busy = aValue;
+    }
+  },
+
+  /**
+   * Set the given window's state to 'not busy'.
+   * @param aWindow the window
+   */
+  _setWindowStateReady: function ssi_setWindowStateReady(aWindow) {
+    this._setWindowStateBusyValue(aWindow, false);
+    this._sendWindowStateEvent(aWindow, "Ready");
+  },
+
+  /**
+   * Set the given window's state to 'busy'.
+   * @param aWindow the window
+   */
+  _setWindowStateBusy: function ssi_setWindowStateBusy(aWindow) {
+    this._setWindowStateBusyValue(aWindow, true);
+    this._sendWindowStateEvent(aWindow, "Busy");
+  },
+
+  /**
+   * Dispatch an SSWindowState_____ event for the given window.
+   * @param aWindow the window
+   * @param aType the type of event, SSWindowState will be prepended to this string
+   */
+  _sendWindowStateEvent: function ssi_sendWindowStateEvent(aWindow, aType) {
+    let event = aWindow.document.createEvent("Events");
+    event.initEvent("SSWindowState" + aType, true, false);
+    aWindow.dispatchEvent(event);
+  },
+
+  /**
+   * Dispatch the SSTabRestored event for the given tab.
+   * @param aTab the which has been restored
+   */
+  _sendTabRestoredNotification: function ssi_sendTabRestoredNotification(aTab) {
+    let event = aTab.ownerDocument.createEvent("Events");
+    event.initEvent("SSTabRestored", true, false);
+    aTab.dispatchEvent(event);
+  },
+
+  /**
+   * @param aWindow
+   *        Window reference
+   * @returns whether this window's data is still cached in _statesToRestore
+   *          because it's not fully loaded yet
+   */
+  _isWindowLoaded: function ssi_isWindowLoaded(aWindow) {
+    return !aWindow.__SS_restoreID;
+  },
+
+  /**
+   * Replace "Loading..." with the tab label (with minimal side-effects)
+   * @param aString is the string the title is stored in
+   * @param aTabbrowser is a tabbrowser object, containing aTab
+   * @param aTab is the tab whose title we're updating & using
+   *
+   * @returns aString that has been updated with the new title
+   */
+  _replaceLoadingTitle : function ssi_replaceLoadingTitle(aString, aTabbrowser, aTab) {
+    if (aString == aTabbrowser.mStringBundle.getString("tabs.connecting")) {
+      aTabbrowser.setTabTitle(aTab);
+      [aString, aTab.label] = [aTab.label, aString];
+    }
+    return aString;
+  },
+
+  /**
+   * Resize this._closedWindows to the value of the pref, except in the case
+   * where we don't have any non-popup windows on Windows and Linux. Then we must
+   * resize such that we have at least one non-popup window.
+   */
+  _capClosedWindows : function ssi_capClosedWindows() {
+    if (this._closedWindows.length <= this._max_windows_undo)
+      return;
+    let spliceTo = this._max_windows_undo;
+#ifndef XP_MACOSX
+    let normalWindowIndex = 0;
+    // try to find a non-popup window in this._closedWindows
+    while (normalWindowIndex < this._closedWindows.length &&
+           !!this._closedWindows[normalWindowIndex].isPopup)
+      normalWindowIndex++;
+    if (normalWindowIndex >= this._max_windows_undo)
+      spliceTo = normalWindowIndex + 1;
+#endif
+    this._closedWindows.splice(spliceTo, this._closedWindows.length);
+  },
+
+  /**
+   * Clears the set of windows that are "resurrected" before writing to disk to
+   * make closing windows one after the other until shutdown work as expected.
+   *
+   * This function should only be called when we are sure that there has been
+   * a user action that indicates the browser is actively being used and all
+   * windows that have been closed before are not part of a series of closing
+   * windows.
+   */
+  _clearRestoringWindows: function ssi_clearRestoringWindows() {
+    for (let i = 0; i < this._closedWindows.length; i++) {
+      delete this._closedWindows[i]._shouldRestore;
+    }
+  },
+
+  /**
+   * Reset state to prepare for a new session state to be restored.
+   */
+  _resetRestoringState: function ssi_initRestoringState() {
+    TabRestoreQueue.reset();
+    this._tabsRestoringCount = 0;
+  },
+
+  /**
+   * Reset the restoring state for a particular tab. This will be called when
+   * removing a tab or when a tab needs to be reset (it's being overwritten).
+   *
+   * @param aTab
+   *        The tab that will be "reset"
+   */
+  _resetLocalTabRestoringState: function (aTab) {
+    let window = aTab.ownerDocument.defaultView;
+    let browser = aTab.linkedBrowser;
+
+    // Keep the tab's previous state for later in this method
+    let previousState = browser.__SS_restoreState;
+
+    // The browser is no longer in any sort of restoring state.
+    delete browser.__SS_restoreState;
+    this._browserEpochs.delete(browser.permanentKey);
+
+    aTab.removeAttribute("pending");
+    browser.removeAttribute("pending");
+
+    if (previousState == TAB_STATE_RESTORING) {
+      if (this._tabsRestoringCount)
+        this._tabsRestoringCount--;
+    } else if (previousState == TAB_STATE_NEEDS_RESTORE) {
+      // Make sure that the tab is removed from the list of tabs to restore.
+      // Again, this is normally done in restoreTabContent, but that isn't being called
+      // for this tab.
+      TabRestoreQueue.remove(aTab);
+    }
+  },
+
+  _resetTabRestoringState: function (tab) {
+    let browser = tab.linkedBrowser;
+    if (browser.__SS_restoreState) {
+      browser.messageManager.sendAsyncMessage("SessionStore:resetRestore", {});
+    }
+    this._resetLocalTabRestoringState(tab);
+  },
+
+  /**
+   * Each time a <browser> element is restored, we increment its "epoch". To
+   * check if a message from content-sessionStore.js is out of date, we can
+   * compare the epoch received with the message to the <browser> element's
+   * epoch. This function does that, and returns true if |epoch| is up-to-date
+   * with respect to |browser|.
+   */
+  isCurrentEpoch: function (browser, epoch) {
+    return this._browserEpochs.get(browser.permanentKey, 0) == epoch;
+  },
+
+};
+
+/**
+ * Priority queue that keeps track of a list of tabs to restore and returns
+ * the tab we should restore next, based on priority rules. We decide between
+ * pinned, visible and hidden tabs in that and FIFO order. Hidden tabs are only
+ * restored with restore_hidden_tabs=true.
+ */
+let TabRestoreQueue = {
+  // The separate buckets used to store tabs.
+  tabs: {priority: [], visible: [], hidden: []},
+
+  // Preferences used by the TabRestoreQueue to determine which tabs
+  // are restored automatically and which tabs will be on-demand.
+  prefs: {
+    // Lazy getter that returns whether tabs are restored on demand.
+    get restoreOnDemand() {
+      let updateValue = () => {
+        let value = Services.prefs.getBoolPref(PREF);
+        let definition = {value: value, configurable: true};
+        Object.defineProperty(this, "restoreOnDemand", definition);
+        return value;
+      }
+
+      const PREF = "browser.sessionstore.restore_on_demand";
+      Services.prefs.addObserver(PREF, updateValue, false);
+      return updateValue();
+    },
+
+    // Lazy getter that returns whether pinned tabs are restored on demand.
+    get restorePinnedTabsOnDemand() {
+      let updateValue = () => {
+        let value = Services.prefs.getBoolPref(PREF);
+        let definition = {value: value, configurable: true};
+        Object.defineProperty(this, "restorePinnedTabsOnDemand", definition);
+        return value;
+      }
+
+      const PREF = "browser.sessionstore.restore_pinned_tabs_on_demand";
+      Services.prefs.addObserver(PREF, updateValue, false);
+      return updateValue();
+    },
+
+    // Lazy getter that returns whether we should restore hidden tabs.
+    get restoreHiddenTabs() {
+      let updateValue = () => {
+        let value = Services.prefs.getBoolPref(PREF);
+        let definition = {value: value, configurable: true};
+        Object.defineProperty(this, "restoreHiddenTabs", definition);
+        return value;
+      }
+
+      const PREF = "browser.sessionstore.restore_hidden_tabs";
+      Services.prefs.addObserver(PREF, updateValue, false);
+      return updateValue();
+    }
+  },
+
+  // Resets the queue and removes all tabs.
+  reset: function () {
+    this.tabs = {priority: [], visible: [], hidden: []};
+  },
+
+  // Adds a tab to the queue and determines its priority bucket.
+  add: function (tab) {
+    let {priority, hidden, visible} = this.tabs;
+
+    if (tab.pinned) {
+      priority.push(tab);
+    } else if (tab.hidden) {
+      hidden.push(tab);
+    } else {
+      visible.push(tab);
+    }
+  },
+
+  // Removes a given tab from the queue, if it's in there.
+  remove: function (tab) {
+    let {priority, hidden, visible} = this.tabs;
+
+    // We'll always check priority first since we don't
+    // have an indicator if a tab will be there or not.
+    let set = priority;
+    let index = set.indexOf(tab);
+
+    if (index == -1) {
+      set = tab.hidden ? hidden : visible;
+      index = set.indexOf(tab);
+    }
+
+    if (index > -1) {
+      set.splice(index, 1);
+    }
+  },
+
+  // Returns and removes the tab with the highest priority.
+  shift: function () {
+    let set;
+    let {priority, hidden, visible} = this.tabs;
+
+    let {restoreOnDemand, restorePinnedTabsOnDemand} = this.prefs;
+    let restorePinned = !(restoreOnDemand && restorePinnedTabsOnDemand);
+    if (restorePinned && priority.length) {
+      set = priority;
+    } else if (!restoreOnDemand) {
+      if (visible.length) {
+        set = visible;
+      } else if (this.prefs.restoreHiddenTabs && hidden.length) {
+        set = hidden;
+      }
+    }
+
+    return set && set.shift();
+  },
+
+  // Moves a given tab from the 'hidden' to the 'visible' bucket.
+  hiddenToVisible: function (tab) {
+    let {hidden, visible} = this.tabs;
+    let index = hidden.indexOf(tab);
+
+    if (index > -1) {
+      hidden.splice(index, 1);
+      visible.push(tab);
+    } else {
+      throw new Error("restore queue: hidden tab not found");
+    }
+  },
+
+  // Moves a given tab from the 'visible' to the 'hidden' bucket.
+  visibleToHidden: function (tab) {
+    let {visible, hidden} = this.tabs;
+    let index = visible.indexOf(tab);
+
+    if (index > -1) {
+      visible.splice(index, 1);
+      hidden.push(tab);
+    } else {
+      throw new Error("restore queue: visible tab not found");
+    }
+  }
+};
+
+// A map storing a closed window's state data until it goes aways (is GC'ed).
+// This ensures that API clients can still read (but not write) states of
+// windows they still hold a reference to but we don't.
+let DyingWindowCache = {
+  _data: new WeakMap(),
+
+  has: function (window) {
+    return this._data.has(window);
+  },
+
+  get: function (window) {
+    return this._data.get(window);
+  },
+
+  set: function (window, data) {
+    this._data.set(window, data);
+  },
+
+  remove: function (window) {
+    this._data.delete(window);
+  }
+};
+
+// A weak set of dirty windows. We use it to determine which windows we need to
+// recollect data for when getCurrentState() is called.
+let DirtyWindows = {
+  _data: new WeakMap(),
+
+  has: function (window) {
+    return this._data.has(window);
+  },
+
+  add: function (window) {
+    return this._data.set(window, true);
+  },
+
+  remove: function (window) {
+    this._data.delete(window);
+  },
+
+  clear: function (window) {
+    this._data.clear();
+  }
+};
+
+// The state from the previous session (after restoring pinned tabs). This
+// state is persisted and passed through to the next session during an app
+// restart to make the third party add-on warning not trash the deferred
+// session
+let LastSession = {
+  _state: null,
+
+  get canRestore() {
+    return !!this._state;
+  },
+
+  getState: function () {
+    return this._state;
+  },
+
+  setState: function (state) {
+    this._state = state;
+  },
+
+  clear: function () {
+    if (this._state) {
+      this._state = null;
+      Services.obs.notifyObservers(null, NOTIFY_LAST_SESSION_CLEARED, null);
+    }
+  }
+};