diff -r 000000000000 -r 6474c204b198 toolkit/components/thumbnails/content/backgroundPageThumbsContent.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/thumbnails/content/backgroundPageThumbsContent.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,171 @@
+/* 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 () { // bug 673569 workaround :(
+
+const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
+
+Cu.import("resource://gre/modules/PageThumbs.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+Cu.import("resource://gre/modules/Services.jsm");
+
+const STATE_LOADING = 1;
+const STATE_CAPTURING = 2;
+const STATE_CANCELED = 3;
+
+const backgroundPageThumbsContent = {
+
+  init: function () {
+    Services.obs.addObserver(this, "document-element-inserted", true);
+
+    // We want a low network priority for this service - lower than b/g tabs
+    // etc - so set it to the lowest priority available.
+    this._webNav.QueryInterface(Ci.nsIDocumentLoader).
+      loadGroup.QueryInterface(Ci.nsISupportsPriority).
+      priority = Ci.nsISupportsPriority.PRIORITY_LOWEST;
+
+    docShell.allowMedia = false;
+    docShell.allowPlugins = false;
+    docShell.allowContentRetargeting = false;
+    let defaultFlags = Ci.nsIRequest.LOAD_ANONYMOUS |
+                       Ci.nsIRequest.LOAD_BYPASS_CACHE |
+                       Ci.nsIRequest.INHIBIT_CACHING |
+                       Ci.nsIWebNavigation.LOAD_FLAGS_BYPASS_HISTORY;
+    docShell.defaultLoadFlags = defaultFlags;
+
+    addMessageListener("BackgroundPageThumbs:capture",
+                       this._onCapture.bind(this));
+    docShell.
+      QueryInterface(Ci.nsIInterfaceRequestor).
+      getInterface(Ci.nsIWebProgress).
+      addProgressListener(this, Ci.nsIWebProgress.NOTIFY_STATE_WINDOW);
+  },
+
+  observe: function (subj, topic, data) {
+    // Arrange to prevent (most) popup dialogs for this window - popups done
+    // in the parent (eg, auth) aren't prevented, but alert() etc are.
+    // disableDialogs only works on the current inner window, so it has
+    // to be called every page load, but before scripts run.
+    if (subj == content.document) {
+      content.
+        QueryInterface(Ci.nsIInterfaceRequestor).
+        getInterface(Ci.nsIDOMWindowUtils).
+        disableDialogs();
+    }
+  },
+
+  get _webNav() {
+    return docShell.QueryInterface(Ci.nsIWebNavigation);
+  },
+
+  _onCapture: function (msg) {
+    this._nextCapture = {
+      id: msg.data.id,
+      url: msg.data.url,
+    };
+    if (this._currentCapture) {
+      if (this._state == STATE_LOADING) {
+        // Cancel the current capture.
+        this._state = STATE_CANCELED;
+        this._loadAboutBlank();
+      }
+      // Let the current capture finish capturing, or if it was just canceled,
+      // wait for onStateChange due to the about:blank load.
+      return;
+    }
+    this._startNextCapture();
+  },
+
+  _startNextCapture: function () {
+    if (!this._nextCapture)
+      return;
+    this._currentCapture = this._nextCapture;
+    delete this._nextCapture;
+    this._state = STATE_LOADING;
+    this._currentCapture.pageLoadStartDate = new Date();
+    this._webNav.loadURI(this._currentCapture.url,
+                         Ci.nsIWebNavigation.LOAD_FLAGS_STOP_CONTENT,
+                         null, null, null);
+  },
+
+  onStateChange: function (webProgress, req, flags, status) {
+    if (webProgress.isTopLevel &&
+        (flags & Ci.nsIWebProgressListener.STATE_STOP) &&
+        this._currentCapture) {
+      if (req.name == "about:blank") {
+        if (this._state == STATE_CAPTURING) {
+          // about:blank has loaded, ending the current capture.
+          this._finishCurrentCapture();
+          delete this._currentCapture;
+          this._startNextCapture();
+        }
+        else if (this._state == STATE_CANCELED) {
+          // A capture request was received while the current capture's page
+          // was still loading.
+          delete this._currentCapture;
+          this._startNextCapture();
+        }
+      }
+      else if (this._state == STATE_LOADING) {
+        // The requested page has loaded.  Capture it.
+        this._state = STATE_CAPTURING;
+        this._captureCurrentPage();
+      }
+    }
+  },
+
+  _captureCurrentPage: function () {
+    let capture = this._currentCapture;
+    capture.finalURL = this._webNav.currentURI.spec;
+    capture.pageLoadTime = new Date() - capture.pageLoadStartDate;
+
+    let canvas = PageThumbs._createCanvas(content);
+    let canvasDrawDate = new Date();
+    PageThumbs._captureToCanvas(content, canvas);
+    capture.canvasDrawTime = new Date() - canvasDrawDate;
+
+    canvas.toBlob(blob => {
+      capture.imageBlob = blob;
+      // Load about:blank to finish the capture and wait for onStateChange.
+      this._loadAboutBlank();
+    });
+  },
+
+  _finishCurrentCapture: function () {
+    let capture = this._currentCapture;
+    let fileReader = Cc["@mozilla.org/files/filereader;1"].
+                     createInstance(Ci.nsIDOMFileReader);
+    fileReader.onloadend = () => {
+      sendAsyncMessage("BackgroundPageThumbs:didCapture", {
+        id: capture.id,
+        imageData: fileReader.result,
+        finalURL: capture.finalURL,
+        telemetry: {
+          CAPTURE_PAGE_LOAD_TIME_MS: capture.pageLoadTime,
+          CAPTURE_CANVAS_DRAW_TIME_MS: capture.canvasDrawTime,
+        },
+      });
+    };
+    fileReader.readAsArrayBuffer(capture.imageBlob);
+  },
+
+  // We load about:blank to finish all captures, even canceled captures.  Two
+  // reasons: GC the captured page, and ensure it can't possibly load any more
+  // resources.
+  _loadAboutBlank: function _loadAboutBlank() {
+    this._webNav.loadURI("about:blank",
+                         Ci.nsIWebNavigation.LOAD_FLAGS_STOP_CONTENT,
+                         null, null, null);
+  },
+
+  QueryInterface: XPCOMUtils.generateQI([
+    Ci.nsIWebProgressListener,
+    Ci.nsISupportsWeakReference,
+    Ci.nsIObserver,
+  ]),
+};
+
+backgroundPageThumbsContent.init();
+
+})();