diff -r 000000000000 -r 6474c204b198 browser/components/sessionstore/test/browser_490040.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/sessionstore/test/browser_490040.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,123 @@
+/* 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/. */
+
+function test() {
+  /** Test for Bug 490040 **/
+
+  waitForExplicitFinish();
+
+  function testWithState(aState) {
+    // Ensure we can store the window if needed.
+    let curClosedWindowCount = ss.getClosedWindowCount();
+    gPrefService.setIntPref("browser.sessionstore.max_windows_undo",
+                            curClosedWindowCount + 1);
+
+    var origWin;
+    function windowObserver(aSubject, aTopic, aData) {
+      let theWin = aSubject.QueryInterface(Ci.nsIDOMWindow);
+      if (origWin && theWin != origWin)
+        return;
+
+      switch (aTopic) {
+        case "domwindowopened":
+          origWin = theWin;
+          theWin.addEventListener("load", function () {
+            theWin.removeEventListener("load", arguments.callee, false);
+            executeSoon(function () {
+              // Close the window as soon as the first tab loads, or
+              // immediately if there are no tabs.
+              if (aState.windowState.windows[0].tabs[0].entries.length) {
+                theWin.gBrowser.addEventListener("load", function() {
+                  theWin.gBrowser.removeEventListener("load",
+                                                      arguments.callee, true);
+                  theWin.close();
+                }, true);
+              } else {
+                executeSoon(function () {
+                  theWin.close();
+                });
+              }
+              ss.setWindowState(theWin, JSON.stringify(aState.windowState),
+                                true);
+            });
+          }, false);
+          break;
+
+        case "domwindowclosed":
+          Services.ww.unregisterNotification(windowObserver);
+          // Use executeSoon to ensure this happens after SS observer.
+          executeSoon(function () {
+            is(ss.getClosedWindowCount(),
+               curClosedWindowCount + (aState.shouldBeAdded ? 1 : 0),
+               "That window should " + (aState.shouldBeAdded ? "" : "not ") +
+               "be restorable");
+            executeSoon(runNextTest);
+          });
+          break;
+      }
+    }
+    Services.ww.registerNotification(windowObserver);
+    Services.ww.openWindow(null,
+                           location,
+                           "_blank",
+                           "chrome,all,dialog=no",
+                           null);
+  }
+
+  // Only windows with open tabs are restorable. Windows where a lone tab is
+  // detached may have _closedTabs, but is left with just an empty tab.
+  let states = [
+    {
+      shouldBeAdded: true,
+      windowState: {
+        windows: [{
+          tabs: [{ entries: [{ url: "http://example.com", title: "example.com" }] }],
+          selected: 1,
+          _closedTabs: []
+        }]
+      }
+    },
+    {
+      shouldBeAdded: false,
+      windowState: {
+        windows: [{
+          tabs: [{ entries: [] }],
+          _closedTabs: []
+        }]
+      }
+    },
+    {
+      shouldBeAdded: false,
+      windowState: {
+        windows: [{
+          tabs: [{ entries: [] }],
+          _closedTabs: [{ state: { entries: [{ url: "http://example.com", index: 1 }] } }]
+        }]
+      }
+    },
+    {
+      shouldBeAdded: false,
+      windowState: {
+        windows: [{
+          tabs: [{ entries: [] }],
+          _closedTabs: [],
+          extData: { keyname: "pi != " + Math.random() }
+        }]
+      }
+    }
+  ];
+
+  function runNextTest() {
+    if (states.length) {
+      let state = states.shift();
+      testWithState(state);
+    }
+    else {
+      gPrefService.clearUserPref("browser.sessionstore.max_windows_undo");
+      finish();
+    }
+  }
+  runNextTest();
+}
+