diff --git a/browser/base/content/browser-fullZoom.js b/browser/base/content/browser-fullZoom.js
index 574f384b935c..ebcaaa0e0911 100644
--- a/browser/base/content/browser-fullZoom.js
+++ b/browser/base/content/browser-fullZoom.js
@@ -10,15 +10,6 @@
 // From nsEventStateManager.cpp.
 const MOUSE_SCROLL_ZOOM = 3;
 
-Cu.import('resource://gre/modules/ContentPrefInstance.jsm');
-
-function getContentPrefs(aWindow) {
-  let context = aWindow ? aWindow.QueryInterface(Ci.nsIInterfaceRequestor)
-                                 .getInterface(Ci.nsIWebNavigation)
-                                 .QueryInterface(Ci.nsILoadContext) : null;
-  return new ContentPrefInstance(context);
-}
-
 /**
  * Controls the "full zoom" setting and its site-specific preferences.
  */
@@ -26,17 +17,6 @@ var FullZoom = {
   // Identifies the setting in the content prefs database.
   name: "browser.content.full-zoom",
 
-  // The global value (if any) for the setting.  Lazily loaded from the service
-  // when first requested, then updated by the pref change listener as it changes.
-  // If there is no global value, then this should be undefined.
-  get globalValue() {
-    var globalValue = getContentPrefs(gBrowser.contentDocument.defaultView).getPref(null, this.name);
-    if (typeof globalValue != "undefined")
-      globalValue = this._ensureValid(globalValue);
-    delete this.globalValue;
-    return this.globalValue = globalValue;
-  },
-
   // browser.zoom.siteSpecific preference cache
   _siteSpecificPref: undefined,
 
@@ -64,7 +44,9 @@ var FullZoom = {
     window.addEventListener("DOMMouseScroll", this, false);
 
     // Register ourselves with the service so we know when our pref changes.
-    getContentPrefs().addObserver(this.name, this);
+    this._cps2 = Cc["@mozilla.org/content-pref/service;1"].
+                 getService(Ci.nsIContentPrefService2);
+    this._cps2.addObserverForName(this.name, this);
 
     this._siteSpecificPref =
       gPrefService.getBoolPref("browser.zoom.siteSpecific");
@@ -77,7 +59,7 @@ var FullZoom = {
 
   destroy: function FullZoom_destroy() {
     gPrefService.removeObserver("browser.zoom.", this);
-    getContentPrefs().removeObserver(this.name, this);
+    this._cps2.removeObserverForName(this.name, this);
     window.removeEventListener("DOMMouseScroll", this, false);
   },
 
@@ -133,7 +115,14 @@ var FullZoom = {
     // We have to call _applySettingToPref in a timeout because we handle
     // the event before the event state manager has a chance to apply the zoom
     // during nsEventStateManager::PostHandleEvent.
-    window.setTimeout(function (self) { self._applySettingToPref() }, 0, this);
+    //
+    // Since the zoom will have already been updated by the time
+    // _applySettingToPref is called, pass true to suppress updating the zoom
+    // again.  Note that this is not an optimization: due to asynchronicity of
+    // the content preference service, the zoom may have been updated again by
+    // the time that onContentPrefSet is called as a result of this call to
+    // _applySettingToPref.
+    window.setTimeout(function (self) self._applySettingToPref(true), 0, this);
   },
 
   // nsIObserver
@@ -158,33 +147,53 @@ var FullZoom = {
   // nsIContentPrefObserver
 
   onContentPrefSet: function FullZoom_onContentPrefSet(aGroup, aName, aValue) {
-    let contentPrefs = getContentPrefs(gBrowser.contentDocument.defaultView);
-    if (aGroup == contentPrefs.grouper.group(gBrowser.currentURI))
-      this._applyPrefToSetting(aValue);
-    else if (aGroup == null) {
-      this.globalValue = this._ensureValid(aValue);
-
-      // If the current page doesn't have a site-specific preference,
-      // then its zoom should be set to the new global preference now that
-      // the global preference has changed.
-      if (!contentPrefs.hasPref(gBrowser.currentURI, this.name))
-        this._applyPrefToSetting();
+    if (this._ignoreNextOnContentPrefSet) {
+      delete this._ignoreNextOnContentPrefSet;
+      return;
     }
+    this._onContentPrefChanged(aGroup, aValue);
   },
 
   onContentPrefRemoved: function FullZoom_onContentPrefRemoved(aGroup, aName) {
-    let contentPrefs = getContentPrefs(gBrowser.contentDocument.defaultView);
-    if (aGroup == contentPrefs.grouper.group(gBrowser.currentURI))
-      this._applyPrefToSetting();
-    else if (aGroup == null) {
-      this.globalValue = undefined;
+    this._onContentPrefChanged(aGroup, undefined);
+  },
 
-      // If the current page doesn't have a site-specific preference,
-      // then its zoom should be set to the default preference now that
-      // the global preference has changed.
-      if (!contentPrefs.hasPref(gBrowser.currentURI, this.name))
-        this._applyPrefToSetting();
+  /**
+   * Appropriately updates the zoom level after a content preference has
+   * changed.
+   *
+   * @param aGroup  The group of the changed preference.
+   * @param aValue  The new value of the changed preference.  Pass undefined to
+   *                indicate the preference's removal.
+   */
+  _onContentPrefChanged: function FullZoom__onContentPrefChanged(aGroup, aValue) {
+    if (!gBrowser.currentURI)
+      return;
+
+    let domain = this._cps2.extractDomain(gBrowser.currentURI.spec);
+    if (aGroup) {
+      if (aGroup == domain)
+        this._applyPrefToSetting(aValue);
+      return;
     }
+
+    this._globalValue = aValue === undefined ? aValue :
+                          this._ensureValid(aValue);
+
+    // If the current page doesn't have a site-specific preference, then its
+    // zoom should be set to the new global preference now that the global
+    // preference has changed.
+    let hasPref = false;
+    let ctxt = this._loadContextFromWindow(gBrowser.contentWindow);
+    this._cps2.getByDomainAndName(gBrowser.currentURI.spec, this.name, ctxt, {
+      handleResult: function () hasPref = true,
+      handleCompletion: function () {
+        if (!hasPref &&
+            gBrowser.currentURI &&
+            this._cps2.extractDomain(gBrowser.currentURI.spec) == domain)
+          this._applyPrefToSetting();
+      }.bind(this)
+    });
   },
 
   // location change observer
@@ -201,12 +210,16 @@ var FullZoom = {
    *        (optional) browser object displaying the document
    */
   onLocationChange: function FullZoom_onLocationChange(aURI, aIsTabSwitch, aBrowser) {
-    if (!aURI || (aIsTabSwitch && !this.siteSpecific))
+    if (!aURI || (aIsTabSwitch && !this.siteSpecific)) {
+      this._notifyOnLocationChange();
       return;
+    }
 
     // Avoid the cps roundtrip and apply the default/global pref.
     if (aURI.spec == "about:blank") {
-      this._applyPrefToSetting(undefined, aBrowser);
+      this._applyPrefToSetting(undefined, aBrowser, function () {
+        this._notifyOnLocationChange();
+      }.bind(this));
       return;
     }
 
@@ -215,24 +228,32 @@ var FullZoom = {
     // Media documents should always start at 1, and are not affected by prefs.
     if (!aIsTabSwitch && browser.contentDocument.mozSyntheticDocument) {
       ZoomManager.setZoomForBrowser(browser, 1);
+      this._notifyOnLocationChange();
       return;
     }
 
-    let contentPrefs = getContentPrefs(gBrowser.contentDocument.defaultView);
-    if (contentPrefs.hasCachedPref(aURI, this.name)) {
-      let zoomValue = contentPrefs.getPref(aURI, this.name);
-      this._applyPrefToSetting(zoomValue, browser);
-    } else {
-      var self = this;
-      contentPrefs.getPref(aURI, this.name, function (aResult) {
-        // Check that we're still where we expect to be in case this took a while.
-        // Null check currentURI, since the window may have been destroyed before
-        // we were called.
-        if (browser.currentURI && aURI.equals(browser.currentURI)) {
-          self._applyPrefToSetting(aResult, browser);
-        }
-      });
+    let ctxt = this._loadContextFromWindow(browser.contentWindow);
+    let pref = this._cps2.getCachedByDomainAndName(aURI.spec, this.name, ctxt);
+    if (pref) {
+      this._applyPrefToSetting(pref.value, browser, function () {
+        this._notifyOnLocationChange();
+      }.bind(this));
+      return;
     }
+
+    let value = undefined;
+    this._cps2.getByDomainAndName(aURI.spec, this.name, ctxt, {
+      handleResult: function (resultPref) value = resultPref.value,
+      handleCompletion: function () {
+        if (browser.currentURI &&
+            this._cps2.extractDomain(browser.currentURI.spec) ==
+              this._cps2.extractDomain(aURI.spec)) {
+          this._applyPrefToSetting(value, browser, function () {
+            this._notifyOnLocationChange();
+          }.bind(this));
+        }
+      }.bind(this)
+    });
   },
 
   // update state of zoom type menu item
@@ -246,23 +267,43 @@ var FullZoom = {
   //**************************************************************************//
   // Setting & Pref Manipulation
 
-  reduce: function FullZoom_reduce() {
+  /**
+   * Reduces the zoom level of the page in the current browser.
+   *
+   * @param callback  Optional.  If given, it's asynchronously called when the
+   *                  zoom update completes.
+   */
+  reduce: function FullZoom_reduce(callback) {
     ZoomManager.reduce();
-    this._applySettingToPref();
+    this._applySettingToPref(false, callback);
   },
 
-  enlarge: function FullZoom_enlarge() {
+  /**
+   * Enlarges the zoom level of the page in the current browser.
+   *
+   * @param callback  Optional.  If given, it's asynchronously called when the
+   *                  zoom update completes.
+   */
+  enlarge: function FullZoom_enlarge(callback) {
     ZoomManager.enlarge();
-    this._applySettingToPref();
+    this._applySettingToPref(false, callback);
   },
 
-  reset: function FullZoom_reset() {
-    if (typeof this.globalValue != "undefined")
-      ZoomManager.zoom = this.globalValue;
-    else
-      ZoomManager.reset();
-
-    this._removePref();
+  /**
+   * Sets the zoom level of the page in the current browser to the global zoom
+   * level.
+   *
+   * @param callback  Optional.  If given, it's asynchronously called when the
+   *                  zoom update completes.
+   */
+  reset: function FullZoom_reset(callback) {
+    this._getGlobalValue(gBrowser.contentWindow, function (value) {
+      if (value === undefined)
+        ZoomManager.reset();
+      else
+        ZoomManager.zoom = value;
+      this._removePref(callback);
+    });
   },
 
   /**
@@ -283,38 +324,91 @@ var FullZoom = {
    * So when we apply new zoom values to the browser, we simply set the zoom.
    * We don't check first to see if the new value is the same as the current
    * one.
-   **/
-  _applyPrefToSetting: function FullZoom__applyPrefToSetting(aValue, aBrowser) {
-    if ((!this.siteSpecific) || gInPrintPreviewMode)
+   *
+   * @param aValue     The zoom level value.
+   * @param aBrowser   The browser containing the page whose zoom level is to be
+   *                   set.  If falsey, the currently selected browser is used.
+   * @param aCallback  Optional.  If given, it's asynchronously called when
+   *                   complete.
+   */
+  _applyPrefToSetting: function FullZoom__applyPrefToSetting(aValue, aBrowser, aCallback) {
+    if (!this.siteSpecific || gInPrintPreviewMode) {
+      this._executeSoon(aCallback);
       return;
+    }
 
     var browser = aBrowser || (gBrowser && gBrowser.selectedBrowser);
-    try {
-      if (browser.contentDocument.mozSyntheticDocument)
-        return;
-
-      if (typeof aValue != "undefined")
-        ZoomManager.setZoomForBrowser(browser, this._ensureValid(aValue));
-      else if (typeof this.globalValue != "undefined")
-        ZoomManager.setZoomForBrowser(browser, this.globalValue);
-      else
-        ZoomManager.setZoomForBrowser(browser, 1);
-    }
-    catch(ex) {}
-  },
-
-  _applySettingToPref: function FullZoom__applySettingToPref() {
-    if (!this.siteSpecific || gInPrintPreviewMode ||
-        content.document.mozSyntheticDocument)
+    if (browser.contentDocument.mozSyntheticDocument) {
+      this._executeSoon(aCallback);
       return;
+    }
 
-    var zoomLevel = ZoomManager.zoom;
-    getContentPrefs(gBrowser.contentDocument.defaultView).setPref(gBrowser.currentURI, this.name, zoomLevel);
+    if (aValue !== undefined) {
+      ZoomManager.setZoomForBrowser(browser, this._ensureValid(aValue));
+      this._executeSoon(aCallback);
+      return;
+    }
+
+    this._getGlobalValue(browser.contentWindow, function (value) {
+      if (gBrowser.selectedBrowser == browser)
+        ZoomManager.setZoomForBrowser(browser, value === undefined ? 1 : value);
+      this._executeSoon(aCallback);
+    });
   },
 
-  _removePref: function FullZoom__removePref() {
-    if (!(content.document.mozSyntheticDocument))
-      getContentPrefs(gBrowser.contentDocument.defaultView).removePref(gBrowser.currentURI, this.name);
+  /**
+   * Saves the zoom level of the page in the current browser to the content
+   * prefs store.
+   *
+   * @param suppressZoomChange  Because this method sets a content preference,
+   *                            our onContentPrefSet method is called as a
+   *                            result, which updates the current zoom level.
+   *                            If suppressZoomChange is true, then the next
+   *                            call to onContentPrefSet will not update the
+   *                            zoom level.
+   * @param callback            Optional.  If given, it's asynchronously called
+   *                            when done.
+   */
+  _applySettingToPref: function FullZoom__applySettingToPref(suppressZoomChange, callback) {
+    if (!this.siteSpecific ||
+        gInPrintPreviewMode ||
+        content.document.mozSyntheticDocument) {
+      this._executeSoon(callback);
+      return;
+    }
+
+    this._cps2.set(gBrowser.currentURI.spec, this.name, ZoomManager.zoom,
+                   this._loadContextFromWindow(gBrowser.contentWindow), {
+      handleCompletion: function () {
+        if (suppressZoomChange)
+          // The content preference service calls observers after callbacks, and
+          // it calls both in the same turn of the event loop.  onContentPrefSet
+          // will therefore be called next, in the same turn of the event loop,
+          // and it will check this flag.
+          this._ignoreNextOnContentPrefSet = true;
+        if (callback)
+          callback();
+      }.bind(this)
+    });
+  },
+
+  /**
+   * Removes from the content prefs store the zoom level of the current browser.
+   *
+   * @param callback  Optional.  If given, it's asynchronously called when done.
+   */
+  _removePref: function FullZoom__removePref(callback) {
+    if (content.document.mozSyntheticDocument) {
+      this._executeSoon(callback);
+      return;
+    }
+    let ctxt = this._loadContextFromWindow(gBrowser.contentWindow);
+    this._cps2.removeByDomainAndName(gBrowser.currentURI.spec, this.name, ctxt, {
+      handleCompletion: function () {
+        if (callback)
+          callback();
+      }
+    });
   },
 
 
@@ -322,6 +416,8 @@ var FullZoom = {
   // Utilities
 
   _ensureValid: function FullZoom__ensureValid(aValue) {
+    // Note that undefined is a valid value for aValue that indicates a known-
+    // not-to-exist value.
     if (isNaN(aValue))
       return 1;
 
@@ -332,5 +428,68 @@ var FullZoom = {
       return ZoomManager.MAX;
 
     return aValue;
-  }
+  },
+
+  /**
+   * Gets the global browser.content.full-zoom content preference.
+   *
+   * WARNING: callback may be called synchronously or asynchronously.  The
+   * reason is that it's usually desirable to avoid turns of the event loop
+   * where possible, since they can lead to visible, jarring jumps in zoom
+   * level.  It's not always possible to avoid them, though.  As a convenience,
+   * then, this method takes a callback and returns nothing.
+   *
+   * @param window    The content window pertaining to the zoom.
+   * @param callback  Synchronously or asynchronously called when done.  It's
+   *                  bound to this object (FullZoom) and passed the preference
+   *                  value.
+   */
+  _getGlobalValue: function FullZoom__getGlobalValue(window, callback) {
+    // * !("_globalValue" in this) => global value not yet cached.
+    // * this._globalValue === undefined => global value known not to exist.
+    // * Otherwise, this._globalValue is a number, the global value.
+    if ("_globalValue" in this) {
+      callback.call(this, this._globalValue);
+      return;
+    }
+    let value = undefined;
+    this._cps2.getGlobal(this.name, this._loadContextFromWindow(window), {
+      handleResult: function (pref) value = pref.value,
+      handleCompletion: function () {
+        this._globalValue = this._ensureValid(value);
+        callback.call(this, this._globalValue);
+      }.bind(this)
+    });
+  },
+
+  /**
+   * Gets the load context from the given window.
+   *
+   * @param window  The window whose load context will be returned.
+   * @return        The nsILoadContext of the given window.
+   */
+  _loadContextFromWindow: function FullZoom__loadContextFromWindow(window) {
+    return window.
+           QueryInterface(Ci.nsIInterfaceRequestor).
+           getInterface(Ci.nsIWebNavigation).
+           QueryInterface(Ci.nsILoadContext);
+  },
+
+  /**
+   * Asynchronously broadcasts a "browser-fullZoom:locationChange" notification
+   * so that tests can select tabs, load pages, etc. and be notified when the
+   * zoom levels on those pages change.  The notification is always asynchronous
+   * so that observers are guaranteed a consistent behavior.
+   */
+  _notifyOnLocationChange: function FullZoom__notifyOnLocationChange() {
+    this._executeSoon(function () {
+      Services.obs.notifyObservers(null, "browser-fullZoom:locationChange", "");
+    });
+  },
+
+  _executeSoon: function FullZoom__executeSoon(callback) {
+    if (!callback)
+      return;
+    Services.tm.mainThread.dispatch(callback, Ci.nsIThread.DISPATCH_NORMAL);
+  },
 };
diff --git a/browser/base/content/test/browser_bug386835.js b/browser/base/content/test/browser_bug386835.js
index 46a69ec395c7..ea4ffbc94414 100644
--- a/browser/base/content/test/browser_bug386835.js
+++ b/browser/base/content/test/browser_bug386835.js
@@ -8,136 +8,82 @@ const FORWARD = 1;
 function test() {
   waitForExplicitFinish();
 
-  gTab1 = gBrowser.addTab(gTestPage);
-  gTab2 = gBrowser.addTab();
-  gTab3 = gBrowser.addTab();
-  gBrowser.selectedTab = gTab1;
+  Task.spawn(function () {
+    gTab1 = gBrowser.addTab(gTestPage);
+    gTab2 = gBrowser.addTab();
+    gTab3 = gBrowser.addTab();
 
-  load(gTab1, gTestPage, function () {
-    load(gTab2, gTestPage, secondPageLoaded);
-  });
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab1);
+    yield FullZoomHelper.load(gTab1, gTestPage);
+    yield FullZoomHelper.load(gTab2, gTestPage);
+  }).then(secondPageLoaded, FullZoomHelper.failAndContinue(finish));
 }
 
 function secondPageLoaded() {
-  zoomTest(gTab1, 1, "Initial zoom of tab 1 should be 1");
-  zoomTest(gTab2, 1, "Initial zoom of tab 2 should be 1");
-  zoomTest(gTab3, 1, "Initial zoom of tab 3 should be 1");
+  Task.spawn(function () {
+    FullZoomHelper.zoomTest(gTab1, 1, "Initial zoom of tab 1 should be 1");
+    FullZoomHelper.zoomTest(gTab2, 1, "Initial zoom of tab 2 should be 1");
+    FullZoomHelper.zoomTest(gTab3, 1, "Initial zoom of tab 3 should be 1");
 
-  // Now have three tabs, two with the test page, one blank. Tab 1 is selected
-  // Zoom tab 1
-  FullZoom.enlarge();
-  gLevel = ZoomManager.getZoomForBrowser(gBrowser.getBrowserForTab(gTab1));
+    // Now have three tabs, two with the test page, one blank. Tab 1 is selected
+    // Zoom tab 1
+    yield FullZoomHelper.enlarge();
+    gLevel = ZoomManager.getZoomForBrowser(gBrowser.getBrowserForTab(gTab1));
 
-  ok(gLevel > 1, "New zoom for tab 1 should be greater than 1");
-  zoomTest(gTab2, 1, "Zooming tab 1 should not affect tab 2");
-  zoomTest(gTab3, 1, "Zooming tab 1 should not affect tab 3");
+    ok(gLevel > 1, "New zoom for tab 1 should be greater than 1");
+    FullZoomHelper.zoomTest(gTab2, 1, "Zooming tab 1 should not affect tab 2");
+    FullZoomHelper.zoomTest(gTab3, 1, "Zooming tab 1 should not affect tab 3");
 
-  load(gTab3, gTestPage, thirdPageLoaded);
+    yield FullZoomHelper.load(gTab3, gTestPage);
+  }).then(thirdPageLoaded, FullZoomHelper.failAndContinue(finish));
 }
 
 function thirdPageLoaded() {
-  zoomTest(gTab1, gLevel, "Tab 1 should still be zoomed");
-  zoomTest(gTab2, 1, "Tab 2 should still not be affected");
-  zoomTest(gTab3, gLevel, "Tab 3 should have zoomed as it was loading in the background");
+  Task.spawn(function () {
+    FullZoomHelper.zoomTest(gTab1, gLevel, "Tab 1 should still be zoomed");
+    FullZoomHelper.zoomTest(gTab2, 1, "Tab 2 should still not be affected");
+    FullZoomHelper.zoomTest(gTab3, gLevel, "Tab 3 should have zoomed as it was loading in the background");
 
-  // Switching to tab 2 should update its zoom setting.
-  afterZoom(function() {
-    zoomTest(gTab1, gLevel, "Tab 1 should still be zoomed");
-    zoomTest(gTab2, gLevel, "Tab 2 should be zoomed now");
-    zoomTest(gTab3, gLevel, "Tab 3 should still be zoomed");
+    // Switching to tab 2 should update its zoom setting.
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab2);
+    FullZoomHelper.zoomTest(gTab1, gLevel, "Tab 1 should still be zoomed");
+    FullZoomHelper.zoomTest(gTab2, gLevel, "Tab 2 should be zoomed now");
+    FullZoomHelper.zoomTest(gTab3, gLevel, "Tab 3 should still be zoomed");
 
-    load(gTab1, gTestImage, imageLoaded);
-  });
-
-  gBrowser.selectedTab = gTab2;
+    yield FullZoomHelper.load(gTab1, gTestImage);
+  }).then(imageLoaded, FullZoomHelper.failAndContinue(finish));
 }
 
 function imageLoaded() {
-  zoomTest(gTab1, 1, "Zoom should be 1 when image was loaded in the background");
-  gBrowser.selectedTab = gTab1;
-  zoomTest(gTab1, 1, "Zoom should still be 1 when tab with image is selected");
-
-  executeSoon(imageZoomSwitch);
+  Task.spawn(function () {
+    FullZoomHelper.zoomTest(gTab1, 1, "Zoom should be 1 when image was loaded in the background");
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab1);
+    FullZoomHelper.zoomTest(gTab1, 1, "Zoom should still be 1 when tab with image is selected");
+  }).then(imageZoomSwitch, FullZoomHelper.failAndContinue(finish));
 }
 
 function imageZoomSwitch() {
-  navigate(BACK, function () {
-    navigate(FORWARD, function () {
-      zoomTest(gTab1, 1, "Tab 1 should not be zoomed when an image loads");
+  Task.spawn(function () {
+    yield FullZoomHelper.navigate(BACK);
+    yield FullZoomHelper.navigate(FORWARD);
+    FullZoomHelper.zoomTest(gTab1, 1, "Tab 1 should not be zoomed when an image loads");
 
-      afterZoom(function() {
-        zoomTest(gTab1, 1, "Tab 1 should still not be zoomed when deselected");
-        finishTest();
-      });
-      gBrowser.selectedTab = gTab2;
-    });
-  });
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab2);
+    FullZoomHelper.zoomTest(gTab1, 1, "Tab 1 should still not be zoomed when deselected");
+  }).then(finishTest, FullZoomHelper.failAndContinue(finish));
 }
 
 var finishTestStarted  = false;
 function finishTest() {
-  ok(!finishTestStarted, "finishTest called more than once");
-  finishTestStarted = true;
-  gBrowser.selectedTab = gTab1;
-  FullZoom.reset();
-  gBrowser.removeTab(gTab1);
-  FullZoom.reset();
-  gBrowser.removeTab(gTab2);
-  FullZoom.reset();
-  gBrowser.removeTab(gTab3);
-  finish();
-}
-
-function zoomTest(tab, val, msg) {
-  is(ZoomManager.getZoomForBrowser(tab.linkedBrowser), val, msg);
-}
-
-function load(tab, url, cb) {
-  let didLoad = false;
-  let didZoom = false;
-  tab.linkedBrowser.addEventListener("load", function (event) {
-    event.currentTarget.removeEventListener("load", arguments.callee, true);
-    didLoad = true;
-    if (didZoom)
-      executeSoon(cb);
-  }, true);
-
-  afterZoom(function() {
-    didZoom = true;
-    if (didLoad)
-      executeSoon(cb);
-  });
-
-  tab.linkedBrowser.loadURI(url);
-}
-
-function navigate(direction, cb) {
-  let didPs = false;
-  let didZoom = false;
-  gBrowser.addEventListener("pageshow", function (event) {
-    gBrowser.removeEventListener("pageshow", arguments.callee, true);
-    didPs = true;
-    if (didZoom)
-      executeSoon(cb);
-  }, true);
-
-  afterZoom(function() {
-    didZoom = true;
-    if (didPs)
-      executeSoon(cb);
-  });
-
-  if (direction == BACK)
-    gBrowser.goBack();
-  else if (direction == FORWARD)
-    gBrowser.goForward();
-}
-
-function afterZoom(cb) {
-  let oldSZFB = ZoomManager.setZoomForBrowser;
-  ZoomManager.setZoomForBrowser = function(browser, value) {
-    oldSZFB.call(ZoomManager, browser, value);
-    ZoomManager.setZoomForBrowser = oldSZFB;
-    executeSoon(cb);
-  };
+  Task.spawn(function () {
+    ok(!finishTestStarted, "finishTest called more than once");
+    finishTestStarted = true;
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab1);
+    yield FullZoomHelper.reset();
+    gBrowser.removeTab(gTab1);
+    yield FullZoomHelper.reset();
+    gBrowser.removeTab(gTab2);
+    yield FullZoomHelper.reset();
+    gBrowser.removeTab(gTab3);
+  }).then(finish, FullZoomHelper.failAndContinue(finish));
 }
diff --git a/browser/base/content/test/browser_bug416661.js b/browser/base/content/test/browser_bug416661.js
index f459284eeeba..af0fe24fedcd 100644
--- a/browser/base/content/test/browser_bug416661.js
+++ b/browser/base/content/test/browser_bug416661.js
@@ -1,62 +1,42 @@
 var tabElm, zoomLevel;
 function start_test_prefNotSet() {
-  is(ZoomManager.zoom, 1, "initial zoom level should be 1");
-  FullZoom.enlarge();
+  Task.spawn(function () {
+    is(ZoomManager.zoom, 1, "initial zoom level should be 1");
+    yield FullZoomHelper.enlarge();
 
-  //capture the zoom level to test later
-  zoomLevel = ZoomManager.zoom;
-  isnot(zoomLevel, 1, "zoom level should have changed");
+    //capture the zoom level to test later
+    zoomLevel = ZoomManager.zoom;
+    isnot(zoomLevel, 1, "zoom level should have changed");
 
-  afterZoomAndLoad(continue_test_prefNotSet);
-  content.location = 
-    "http://mochi.test:8888/browser/browser/base/content/test/moz.png";
+    yield FullZoomHelper.load(gBrowser.selectedTab, "http://mochi.test:8888/browser/browser/base/content/test/moz.png");
+  }).then(continue_test_prefNotSet, FullZoomHelper.failAndContinue(finish));
 }
 
 function continue_test_prefNotSet () {
-  is(ZoomManager.zoom, 1, "zoom level pref should not apply to an image");
-  FullZoom.reset();
+  Task.spawn(function () {
+    is(ZoomManager.zoom, 1, "zoom level pref should not apply to an image");
+    yield FullZoomHelper.reset();
 
-  afterZoomAndLoad(end_test_prefNotSet);
-  content.location = 
-    "http://mochi.test:8888/browser/browser/base/content/test/zoom_test.html";
+    yield FullZoomHelper.load(gBrowser.selectedTab, "http://mochi.test:8888/browser/browser/base/content/test/zoom_test.html");
+  }).then(end_test_prefNotSet, FullZoomHelper.failAndContinue(finish));
 }
 
 function end_test_prefNotSet() {
-  is(ZoomManager.zoom, zoomLevel, "the zoom level should have persisted");
+  Task.spawn(function () {
+    is(ZoomManager.zoom, zoomLevel, "the zoom level should have persisted");
 
-  // Reset the zoom so that other tests have a fresh zoom level
-  FullZoom.reset();
-  gBrowser.removeCurrentTab();
-  finish();
+    // Reset the zoom so that other tests have a fresh zoom level
+    yield FullZoomHelper.reset();
+    gBrowser.removeCurrentTab();
+  }).then(finish, FullZoomHelper.failAndContinue(finish));
 }
 
-
 function test() {
   waitForExplicitFinish();
 
-  tabElm = gBrowser.addTab();
-  gBrowser.selectedTab = tabElm;
-
-  afterZoomAndLoad(start_test_prefNotSet);
-  content.location = 
-    "http://mochi.test:8888/browser/browser/base/content/test/zoom_test.html";
-}
-
-function afterZoomAndLoad(cb) {
-  let didLoad = false;
-  let didZoom = false;
-  tabElm.linkedBrowser.addEventListener("load", function() {
-    tabElm.linkedBrowser.removeEventListener("load", arguments.callee, true);
-    didLoad = true;
-    if (didZoom)
-      executeSoon(cb);
-  }, true);
-  let oldSZFB = ZoomManager.setZoomForBrowser;
-  ZoomManager.setZoomForBrowser = function(browser, value) {
-    oldSZFB.call(ZoomManager, browser, value);
-    ZoomManager.setZoomForBrowser = oldSZFB;
-    didZoom = true;
-    if (didLoad)
-      executeSoon(cb);
-  };
+  Task.spawn(function () {
+    tabElm = gBrowser.addTab();
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(tabElm);
+    yield FullZoomHelper.load(tabElm, "http://mochi.test:8888/browser/browser/base/content/test/zoom_test.html");
+  }).then(start_test_prefNotSet, FullZoomHelper.failAndContinue(finish));
 }
diff --git a/browser/base/content/test/browser_bug419612.js b/browser/base/content/test/browser_bug419612.js
index 2ff094873dc8..76194c9f9bc9 100644
--- a/browser/base/content/test/browser_bug419612.js
+++ b/browser/base/content/test/browser_bug419612.js
@@ -1,49 +1,32 @@
 function test() {
   waitForExplicitFinish();
 
-  let testPage = "http://example.org/browser/browser/base/content/test/dummy_page.html";
-  let tab1 = gBrowser.selectedTab = gBrowser.addTab();
-  tab1.linkedBrowser.addEventListener("load", (function(event) {
-    event.currentTarget.removeEventListener("load", arguments.callee, true);
+  Task.spawn(function () {
+    let testPage = "http://example.org/browser/browser/base/content/test/dummy_page.html";
+    let tab1 = gBrowser.addTab();
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(tab1);
+    yield FullZoomHelper.load(tab1, testPage);
 
     let tab2 = gBrowser.addTab();
-    tab2.linkedBrowser.addEventListener("load", (function(event) {
-      event.currentTarget.removeEventListener("load", arguments.callee, true);
+    yield FullZoomHelper.load(tab2, testPage);
 
-      FullZoom.enlarge();
-      let tab1Zoom = ZoomManager.getZoomForBrowser(tab1.linkedBrowser);
+    yield FullZoomHelper.enlarge();
+    let tab1Zoom = ZoomManager.getZoomForBrowser(tab1.linkedBrowser);
 
-      afterZoom(function() {
-        let tab2Zoom = ZoomManager.getZoomForBrowser(tab2.linkedBrowser);
-        is(tab2Zoom, tab1Zoom, "Zoom should affect background tabs");
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(tab2);
+    let tab2Zoom = ZoomManager.getZoomForBrowser(tab2.linkedBrowser);
+    is(tab2Zoom, tab1Zoom, "Zoom should affect background tabs");
 
-        gPrefService.setBoolPref("browser.zoom.updateBackgroundTabs", false);
-        FullZoom.reset();
-        gBrowser.selectedTab = tab1;
-        tab1Zoom = ZoomManager.getZoomForBrowser(tab1.linkedBrowser);
-        tab2Zoom = ZoomManager.getZoomForBrowser(tab2.linkedBrowser);
-        isnot(tab1Zoom, tab2Zoom, "Zoom should not affect background tabs");
+    gPrefService.setBoolPref("browser.zoom.updateBackgroundTabs", false);
+    yield FullZoomHelper.reset();
+    gBrowser.selectedTab = tab1;
+    tab1Zoom = ZoomManager.getZoomForBrowser(tab1.linkedBrowser);
+    tab2Zoom = ZoomManager.getZoomForBrowser(tab2.linkedBrowser);
+    isnot(tab1Zoom, tab2Zoom, "Zoom should not affect background tabs");
 
-        if (gPrefService.prefHasUserValue("browser.zoom.updateBackgroundTabs"))
-          gPrefService.clearUserPref("browser.zoom.updateBackgroundTabs");
-        gBrowser.removeTab(tab1);
-        gBrowser.removeTab(tab2);
-        finish();
-      });
-      gBrowser.selectedTab = tab2;
-    }), true);
-    tab2.linkedBrowser.loadURI(testPage);
-  }), true);
-  content.location = testPage;
-}
-
-function afterZoom(cb) {
-  let oldAPTS = FullZoom._applyPrefToSetting;
-  FullZoom._applyPrefToSetting = function(value, browser) {
-    if (!value)
-      value = undefined;
-    oldAPTS.call(FullZoom, value, browser);
-    FullZoom._applyPrefToSetting = oldAPTS;
-    executeSoon(cb);
-  };
+    if (gPrefService.prefHasUserValue("browser.zoom.updateBackgroundTabs"))
+      gPrefService.clearUserPref("browser.zoom.updateBackgroundTabs");
+    gBrowser.removeTab(tab1);
+    gBrowser.removeTab(tab2);
+  }).then(finish, FullZoomHelper.failAndContinue(finish));
 }
diff --git a/browser/base/content/test/browser_bug441778.js b/browser/base/content/test/browser_bug441778.js
index 7fa37c65e70e..dd51d70e65ba 100644
--- a/browser/base/content/test/browser_bug441778.js
+++ b/browser/base/content/test/browser_bug441778.js
@@ -13,19 +13,22 @@ function test() {
   const TEST_PAGE_URL = 'data:text/html,<body><iframe src=""></iframe></body>';
   const TEST_IFRAME_URL = "http://test2.example.org/";
 
-  // Prepare the test tab
-  gBrowser.selectedTab = gBrowser.addTab();
-  let testBrowser = gBrowser.selectedBrowser;
+  Task.spawn(function () {
+    // Prepare the test tab
+    let tab = gBrowser.addTab();
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(tab);
 
-  testBrowser.addEventListener("load", function () {
-    testBrowser.removeEventListener("load", arguments.callee, true);
+    let testBrowser = tab.linkedBrowser;
+
+    yield FullZoomHelper.load(tab, TEST_PAGE_URL);
 
     // Change the zoom level and then save it so we can compare it to the level
     // after loading the sub-document.
-    FullZoom.enlarge();
+    yield FullZoomHelper.enlarge();
     var zoomLevel = ZoomManager.zoom;
 
     // Start the sub-document load.
+    let deferred = Promise.defer();
     executeSoon(function () {
       testBrowser.addEventListener("load", function (e) {
         testBrowser.removeEventListener("load", arguments.callee, true);
@@ -34,11 +37,10 @@ function test() {
         is(ZoomManager.zoom, zoomLevel, "zoom is retained after sub-document load");
 
         gBrowser.removeCurrentTab();
-        finish();
+        deferred.resolve();
       }, true);
       content.document.querySelector("iframe").src = TEST_IFRAME_URL;
     });
-  }, true);
-
-  content.location = TEST_PAGE_URL;
+    yield deferred.promise;
+  }).then(finish, FullZoomHelper.failAndContinue(finish));
 }
diff --git a/browser/base/content/test/browser_bug555224.js b/browser/base/content/test/browser_bug555224.js
index fa38a471d32a..cff1ee12b6b4 100644
--- a/browser/base/content/test/browser_bug555224.js
+++ b/browser/base/content/test/browser_bug555224.js
@@ -4,59 +4,36 @@
 const TEST_PAGE = "/browser/browser/base/content/test/dummy_page.html";
 var gTestTab, gBgTab, gTestZoom;
 
-function afterZoomAndLoad(aCallback, aTab) {
-  let didLoad = false;
-  let didZoom = false;
-  aTab.linkedBrowser.addEventListener("load", function() {
-    aTab.linkedBrowser.removeEventListener("load", arguments.callee, true);
-    didLoad = true;
-    if (didZoom)
-      executeSoon(aCallback);
-  }, true);
-  let oldAPTS = FullZoom._applyPrefToSetting;
-  FullZoom._applyPrefToSetting = function(value, browser) {
-    if (!value)
-      value = undefined;
-    oldAPTS.call(FullZoom, value, browser);
-    // Don't reset _applyPrefToSetting until we've seen the about:blank load(s)
-    if (browser && browser.currentURI.spec.startsWith("http:")) {
-      FullZoom._applyPrefToSetting = oldAPTS;
-      didZoom = true;
-    }
-    if (didLoad && didZoom)
-      executeSoon(aCallback);
-  };
-}
-
 function testBackgroundLoad() {
-  is(ZoomManager.zoom, gTestZoom, "opening a background tab should not change foreground zoom");
+  Task.spawn(function () {
+    is(ZoomManager.zoom, gTestZoom, "opening a background tab should not change foreground zoom");
 
-  gBrowser.removeTab(gBgTab);
+    gBrowser.removeTab(gBgTab);
 
-  FullZoom.reset();
-  gBrowser.removeTab(gTestTab);
-
-  finish();
+    yield FullZoomHelper.reset();
+    gBrowser.removeTab(gTestTab);
+  }).then(finish, FullZoomHelper.failAndContinue(finish));
 }
 
 function testInitialZoom() {
-  is(ZoomManager.zoom, 1, "initial zoom level should be 1");
-  FullZoom.enlarge();
+  Task.spawn(function () {
+    is(ZoomManager.zoom, 1, "initial zoom level should be 1");
+    yield FullZoomHelper.enlarge();
 
-  gTestZoom = ZoomManager.zoom;
-  isnot(gTestZoom, 1, "zoom level should have changed");
+    gTestZoom = ZoomManager.zoom;
+    isnot(gTestZoom, 1, "zoom level should have changed");
 
-  afterZoomAndLoad(testBackgroundLoad,
-                   gBgTab = gBrowser.loadOneTab("http://mochi.test:8888" + TEST_PAGE,
-                                                {inBackground: true}));
+    gBgTab = gBrowser.addTab();
+    yield FullZoomHelper.load(gBgTab, "http://mochi.test:8888" + TEST_PAGE);
+  }).then(testBackgroundLoad, FullZoomHelper.failAndContinue(finish));
 }
 
 function test() {
   waitForExplicitFinish();
 
-  gTestTab = gBrowser.addTab();
-  gBrowser.selectedTab = gTestTab;
-
-  afterZoomAndLoad(testInitialZoom, gTestTab);
-  content.location = "http://example.org" + TEST_PAGE;
+  Task.spawn(function () {
+    gTestTab = gBrowser.addTab();
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTestTab);
+    yield FullZoomHelper.load(gTestTab, "http://example.org" + TEST_PAGE);
+  }).then(testInitialZoom, FullZoomHelper.failAndContinue(finish));
 }
diff --git a/browser/base/content/test/browser_bug559991.js b/browser/base/content/test/browser_bug559991.js
index 19d6127a0e8a..3bebc16e4f59 100644
--- a/browser/base/content/test/browser_bug559991.js
+++ b/browser/base/content/test/browser_bug559991.js
@@ -1,3 +1,5 @@
+var tab;
+
 function test() {
 
   // ----------
@@ -5,53 +7,34 @@ function test() {
 
   waitForExplicitFinish();
 
-  let oldOLC = FullZoom.onLocationChange;
-  FullZoom.onLocationChange = function(aURI, aIsTabSwitch, aBrowser) {
-    // Ignore calls that are not about tab switching on this test
-    if (aIsTabSwitch)
-      oldOLC.call(FullZoom, aURI, aIsTabSwitch, aBrowser);
-  };
-
   gPrefService.setBoolPref("browser.zoom.updateBackgroundTabs", true);
   gPrefService.setBoolPref("browser.zoom.siteSpecific", true);
 
-  let oldAPTS = FullZoom._applyPrefToSetting;
   let uri = "http://example.org/browser/browser/base/content/test/dummy_page.html";
 
-  let tab = gBrowser.addTab();
-  tab.linkedBrowser.addEventListener("load", function(event) {
-    tab.linkedBrowser.removeEventListener("load", arguments.callee, true);
+  Task.spawn(function () {
+    tab = gBrowser.addTab();
+    yield FullZoomHelper.load(tab, uri);
 
     // -------------------------------------------------------------------
     // Test - Trigger a tab switch that should update the zoom level
-    FullZoom._applyPrefToSetting = function() {
-      ok(true, "applyPrefToSetting was called");
-      endTest();
-    }
-    gBrowser.selectedTab = tab;
-
-  }, true); 
-  tab.linkedBrowser.loadURI(uri);
-
-  // -------------
-  // Test clean-up
-  function endTest() {
-    FullZoom._applyPrefToSetting = oldAPTS;
-    FullZoom.onLocationChange = oldOLC;
-    gBrowser.removeTab(tab);
-
-    oldAPTS = null;
-    oldOLC = null;
-    tab = null;
-
-    if (gPrefService.prefHasUserValue("browser.zoom.updateBackgroundTabs"))
-      gPrefService.clearUserPref("browser.zoom.updateBackgroundTabs");
-
-    if (gPrefService.prefHasUserValue("browser.zoom.siteSpecific"))
-      gPrefService.clearUserPref("browser.zoom.siteSpecific");
-
-    finish();
-  }
-
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(tab);
+    ok(true, "applyPrefToSetting was called");
+  }).then(endTest, FullZoomHelper.failAndContinue(endTest));
 }
 
+// -------------
+// Test clean-up
+function endTest() {
+  gBrowser.removeTab(tab);
+
+  tab = null;
+
+  if (gPrefService.prefHasUserValue("browser.zoom.updateBackgroundTabs"))
+    gPrefService.clearUserPref("browser.zoom.updateBackgroundTabs");
+
+  if (gPrefService.prefHasUserValue("browser.zoom.siteSpecific"))
+    gPrefService.clearUserPref("browser.zoom.siteSpecific");
+
+  finish();
+}
diff --git a/browser/base/content/test/browser_bug575830.js b/browser/base/content/test/browser_bug575830.js
index 9f08d6779f8b..aed13eea5522 100644
--- a/browser/base/content/test/browser_bug575830.js
+++ b/browser/base/content/test/browser_bug575830.js
@@ -13,25 +13,22 @@ function test() {
     gBrowser.removeTab(tab2);
   });
 
-  tab1 = gBrowser.addTab(TEST_IMAGE);
-  tab2 = gBrowser.addTab();
-  gBrowser.selectedTab = tab1;
+  Task.spawn(function () {
+    tab1 = gBrowser.addTab();
+    tab2 = gBrowser.addTab();
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(tab1);
+    yield FullZoomHelper.load(tab1, TEST_IMAGE);
 
-  tab1.linkedBrowser.addEventListener("load", function onload() {
-    tab1.linkedBrowser.removeEventListener("load", onload, true);
     is(ZoomManager.zoom, 1, "initial zoom level for first should be 1");
 
-    FullZoom.enlarge();
+    yield FullZoomHelper.enlarge();
     let zoom = ZoomManager.zoom;
     isnot(zoom, 1, "zoom level should have changed");
 
-    gBrowser.selectedTab = tab2;
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(tab2);
     is(ZoomManager.zoom, 1, "initial zoom level for second tab should be 1");
 
-    gBrowser.selectedTab = tab1;
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(tab1);
     is(ZoomManager.zoom, zoom, "zoom level for first tab should not have changed");
-
-    finish();
-  }, true);
+  }).then(finish, FullZoomHelper.failAndContinue(finish));
 }
-
diff --git a/browser/base/content/test/browser_bug719271.js b/browser/base/content/test/browser_bug719271.js
index 6db54554f50d..53aca641e457 100644
--- a/browser/base/content/test/browser_bug719271.js
+++ b/browser/base/content/test/browser_bug719271.js
@@ -11,131 +11,71 @@ var gTab1, gTab2, gLevel1, gLevel2;
 function test() {
   waitForExplicitFinish();
 
-  gTab1 = gBrowser.addTab();
-  gTab2 = gBrowser.addTab();
-  gBrowser.selectedTab = gTab1;
+  Task.spawn(function () {
+    gTab1 = gBrowser.addTab();
+    gTab2 = gBrowser.addTab();
 
-  load(gTab1, TEST_PAGE, function() {
-    load(gTab2, TEST_VIDEO, zoomTab1);
-  });
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab1);
+    yield FullZoomHelper.load(gTab1, TEST_PAGE);
+    yield FullZoomHelper.load(gTab2, TEST_VIDEO);
+  }).then(zoomTab1, FullZoomHelper.failAndContinue(finish));
 }
 
 function zoomTab1() {
-  is(gBrowser.selectedTab, gTab1, "Tab 1 is selected");
-  zoomTest(gTab1, 1, "Initial zoom of tab 1 should be 1");
-  zoomTest(gTab2, 1, "Initial zoom of tab 2 should be 1");
+  Task.spawn(function () {
+    is(gBrowser.selectedTab, gTab1, "Tab 1 is selected");
+    FullZoomHelper.zoomTest(gTab1, 1, "Initial zoom of tab 1 should be 1");
+    FullZoomHelper.zoomTest(gTab2, 1, "Initial zoom of tab 2 should be 1");
 
-  FullZoom.enlarge();
-  gLevel1 = ZoomManager.getZoomForBrowser(gBrowser.getBrowserForTab(gTab1));
+    yield FullZoomHelper.enlarge();
+    gLevel1 = ZoomManager.getZoomForBrowser(gBrowser.getBrowserForTab(gTab1));
 
-  ok(gLevel1 > 1, "New zoom for tab 1 should be greater than 1");
-  zoomTest(gTab2, 1, "Zooming tab 1 should not affect tab 2");
+    ok(gLevel1 > 1, "New zoom for tab 1 should be greater than 1");
+    FullZoomHelper.zoomTest(gTab2, 1, "Zooming tab 1 should not affect tab 2");
 
-  gBrowser.selectedTab = gTab2;
-  zoomTest(gTab2, 1, "Tab 2 is still unzoomed after it is selected");
-  zoomTest(gTab1, gLevel1, "Tab 1 is still zoomed");
-
-  zoomTab2();
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab2);
+    FullZoomHelper.zoomTest(gTab2, 1, "Tab 2 is still unzoomed after it is selected");
+    FullZoomHelper.zoomTest(gTab1, gLevel1, "Tab 1 is still zoomed");
+  }).then(zoomTab2, FullZoomHelper.failAndContinue(finish));
 }
 
 function zoomTab2() {
-  is(gBrowser.selectedTab, gTab2, "Tab 2 is selected");
+  Task.spawn(function () {
+    is(gBrowser.selectedTab, gTab2, "Tab 2 is selected");
 
-  FullZoom.reduce();
-  let gLevel2 = ZoomManager.getZoomForBrowser(gBrowser.getBrowserForTab(gTab2));
+    yield FullZoomHelper.reduce();
+    let gLevel2 = ZoomManager.getZoomForBrowser(gBrowser.getBrowserForTab(gTab2));
 
-  ok(gLevel2 < 1, "New zoom for tab 2 should be less than 1");
-  zoomTest(gTab1, gLevel1, "Zooming tab 2 should not affect tab 1");
+    ok(gLevel2 < 1, "New zoom for tab 2 should be less than 1");
+    FullZoomHelper.zoomTest(gTab1, gLevel1, "Zooming tab 2 should not affect tab 1");
 
-  afterZoom(function() {
-    zoomTest(gTab1, gLevel1, "Tab 1 should have the same zoom after it's selected");
-
-    testNavigation();
-  });
-  gBrowser.selectedTab = gTab1;
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab1);
+    FullZoomHelper.zoomTest(gTab1, gLevel1, "Tab 1 should have the same zoom after it's selected");
+  }).then(testNavigation, FullZoomHelper.failAndContinue(finish));
 }
 
 function testNavigation() {
-  load(gTab1, TEST_VIDEO, function() {
-    zoomTest(gTab1, 1, "Zoom should be 1 when a video was loaded");
-    navigate(BACK, function() {
-      zoomTest(gTab1, gLevel1, "Zoom should be restored when a page is loaded");
-      navigate(FORWARD, function() {
-        zoomTest(gTab1, 1, "Zoom should be 1 again when navigating back to a video");
-        finishTest();
-      });
-    });
-  });
+  Task.spawn(function () {
+    yield FullZoomHelper.load(gTab1, TEST_VIDEO);
+    FullZoomHelper.zoomTest(gTab1, 1, "Zoom should be 1 when a video was loaded");
+    yield FullZoomHelper.navigate(FullZoomHelper.BACK);
+    FullZoomHelper.zoomTest(gTab1, gLevel1, "Zoom should be restored when a page is loaded");
+    yield FullZoomHelper.navigate(FullZoomHelper.FORWARD);
+    FullZoomHelper.zoomTest(gTab1, 1, "Zoom should be 1 again when navigating back to a video");
+  }).then(finishTest, FullZoomHelper.failAndContinue(finish));
 }
 
 var finishTestStarted  = false;
 function finishTest() {
-  ok(!finishTestStarted, "finishTest called more than once");
-  finishTestStarted = true;
+  Task.spawn(function () {
+    ok(!finishTestStarted, "finishTest called more than once");
+    finishTestStarted = true;
 
-  gBrowser.selectedTab = gTab1;
-  FullZoom.reset();
-  gBrowser.removeTab(gTab1);
-
-  gBrowser.selectedTab = gTab2;
-  FullZoom.reset();
-  gBrowser.removeTab(gTab2);
-
-  finish();
-}
-
-function zoomTest(tab, val, msg) {
-  is(ZoomManager.getZoomForBrowser(tab.linkedBrowser), val, msg);
-}
-
-function load(tab, url, cb) {
-  let didLoad = false;
-  let didZoom = false;
-  tab.linkedBrowser.addEventListener("load", function onload(event) {
-    event.currentTarget.removeEventListener("load", onload, true);
-    didLoad = true;
-    if (didZoom)
-      executeSoon(cb);
-  }, true);
-
-  afterZoom(function() {
-    didZoom = true;
-    if (didLoad)
-      executeSoon(cb);
-  });
-
-  tab.linkedBrowser.loadURI(url);
-}
-
-const BACK = 0;
-const FORWARD = 1;
-function navigate(direction, cb) {
-  let didPs = false;
-  let didZoom = false;
-  gBrowser.addEventListener("pageshow", function onpageshow(event) {
-    gBrowser.removeEventListener("pageshow", onpageshow, true);
-    didPs = true;
-    if (didZoom)
-      executeSoon(cb);
-  }, true);
-
-  afterZoom(function() {
-    didZoom = true;
-    if (didPs)
-      executeSoon(cb);
-  });
-
-  if (direction == BACK)
-    gBrowser.goBack();
-  else if (direction == FORWARD)
-    gBrowser.goForward();
-}
-
-function afterZoom(cb) {
-  let oldSZFB = ZoomManager.setZoomForBrowser;
-  ZoomManager.setZoomForBrowser = function(browser, value) {
-    oldSZFB.call(ZoomManager, browser, value);
-    ZoomManager.setZoomForBrowser = oldSZFB;
-    executeSoon(cb);
-  };
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab1);
+    yield FullZoomHelper.reset();
+    gBrowser.removeTab(gTab1);
+    yield FullZoomHelper.selectTabAndWaitForLocationChange(gTab2);
+    yield FullZoomHelper.reset();
+    gBrowser.removeTab(gTab2);
+  }).then(finish, FullZoomHelper.failAndContinue(finish));
 }
diff --git a/browser/base/content/test/head.js b/browser/base/content/test/head.js
index 8570e1613e12..43107dbd71be 100644
--- a/browser/base/content/test/head.js
+++ b/browser/base/content/test/head.js
@@ -261,3 +261,107 @@ function promiseHistoryClearedState(aURIs, aShouldBeCleared) {
 
   return deferred.promise;
 }
+
+let FullZoomHelper = {
+
+  selectTabAndWaitForLocationChange: function selectTabAndWaitForLocationChange(tab) {
+    let deferred = Promise.defer();
+    if (tab && gBrowser.selectedTab == tab) {
+      deferred.resolve();
+      return deferred.promise;
+    }
+    if (tab)
+      gBrowser.selectedTab = tab;
+    Services.obs.addObserver(function obs() {
+      Services.obs.removeObserver(obs, "browser-fullZoom:locationChange");
+      deferred.resolve();
+    }, "browser-fullZoom:locationChange", false);
+    return deferred.promise;
+  },
+
+  load: function load(tab, url) {
+    let deferred = Promise.defer();
+    let didLoad = false;
+    let didZoom = false;
+
+    tab.linkedBrowser.addEventListener("load", function (event) {
+      event.currentTarget.removeEventListener("load", arguments.callee, true);
+      didLoad = true;
+      if (didZoom)
+        deferred.resolve();
+    }, true);
+
+    // Don't select background tabs.  That way tests can use this method on
+    // background tabs without having them automatically be selected.  Just wait
+    // for the zoom to change on the current tab if it's `tab`.
+    if (tab == gBrowser.selectedTab) {
+      this.selectTabAndWaitForLocationChange(null).then(function () {
+        didZoom = true;
+        if (didLoad)
+          deferred.resolve();
+      });
+    }
+    else
+      didZoom = true;
+
+    tab.linkedBrowser.loadURI(url);
+
+    return deferred.promise;
+  },
+
+  zoomTest: function zoomTest(tab, val, msg) {
+    is(ZoomManager.getZoomForBrowser(tab.linkedBrowser), val, msg);
+  },
+
+  enlarge: function enlarge() {
+    let deferred = Promise.defer();
+    FullZoom.enlarge(function () deferred.resolve());
+    return deferred.promise;
+  },
+
+  reduce: function reduce() {
+    let deferred = Promise.defer();
+    FullZoom.reduce(function () deferred.resolve());
+    return deferred.promise;
+  },
+
+  reset: function reset() {
+    let deferred = Promise.defer();
+    FullZoom.reset(function () deferred.resolve());
+    return deferred.promise;
+  },
+
+  BACK: 0,
+  FORWARD: 1,
+  navigate: function navigate(direction) {
+    let deferred = Promise.defer();
+    let didPs = false;
+    let didZoom = false;
+
+    gBrowser.addEventListener("pageshow", function (event) {
+      gBrowser.removeEventListener("pageshow", arguments.callee, true);
+      didPs = true;
+      if (didZoom)
+        deferred.resolve();
+    }, true);
+
+    if (direction == this.BACK)
+      gBrowser.goBack();
+    else if (direction == this.FORWARD)
+      gBrowser.goForward();
+
+    this.selectTabAndWaitForLocationChange(null).then(function () {
+      didZoom = true;
+      if (didPs)
+        deferred.resolve();
+    });
+    return deferred.promise;
+  },
+
+  failAndContinue: function failAndContinue(func) {
+    return function (err) {
+      ok(false, err);
+      func();
+    };
+  },
+};
diff --git a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_zoom.js b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_zoom.js
index cf4df0301ab6..827b915629d4 100644
--- a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_zoom.js
+++ b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_zoom.js
@@ -25,27 +25,29 @@ function test() {
           let mozillaZoom = aWindow.ZoomManager.zoom;
 
           // change the zoom on the mozilla page
-          aWindow.FullZoom.enlarge();
-          // make sure the zoom level has been changed
-          isnot(aWindow.ZoomManager.zoom, mozillaZoom, "Zoom level can be changed");
-          mozillaZoom = aWindow.ZoomManager.zoom;
+          aWindow.FullZoom.enlarge(function () {
+            // make sure the zoom level has been changed
+            isnot(aWindow.ZoomManager.zoom, mozillaZoom, "Zoom level can be changed");
+            mozillaZoom = aWindow.ZoomManager.zoom;
 
-          // switch to about: tab
-          aWindow.gBrowser.selectedTab = tabAbout;
+            // switch to about: tab
+            aWindow.gBrowser.selectedTab = tabAbout;
 
-          // switch back to mozilla tab
-          aWindow.gBrowser.selectedTab = tabMozilla;
+            // switch back to mozilla tab
+            aWindow.gBrowser.selectedTab = tabMozilla;
 
-          // make sure the zoom level has not changed
-          is(aWindow.ZoomManager.zoom, mozillaZoom,
-            "Entering private browsing should not reset the zoom on a tab");
+            // make sure the zoom level has not changed
+            is(aWindow.ZoomManager.zoom, mozillaZoom,
+              "Entering private browsing should not reset the zoom on a tab");
 
-          // cleanup
-          aWindow.FullZoom.reset();
-          aWindow.gBrowser.removeTab(tabMozilla);
-          aWindow.gBrowser.removeTab(tabAbout);
-          aWindow.close();
-          aCallback();
+            // cleanup
+            aWindow.FullZoom.reset(function () {
+              aWindow.gBrowser.removeTab(tabMozilla);
+              aWindow.gBrowser.removeTab(tabAbout);
+              aWindow.close();
+              aCallback();
+            });
+          });
         }, true);
         mozillaBrowser.contentWindow.location = "about:mozilla";
       }, true);
diff --git a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_zoomrestore.js b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_zoomrestore.js
index 46a5ba76624d..9bac502a35a7 100644
--- a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_zoomrestore.js
+++ b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_zoomrestore.js
@@ -16,12 +16,14 @@ function test() {
       aWindow.gBrowser.selectedBrowser.removeEventListener("load", onLoad, true);
       if (aIsZoomedWindow) {
         // change the zoom on the blank page
-        aWindow.FullZoom.enlarge();
-        isnot(aWindow.ZoomManager.zoom, 1, "Zoom level for about:blank should be changed");
-      } else {
-        // make sure the zoom level is set to 1
-        is(aWindow.ZoomManager.zoom, 1, "Zoom level for about:privatebrowsing should be reset");
+        aWindow.FullZoom.enlarge(function () {
+          isnot(aWindow.ZoomManager.zoom, 1, "Zoom level for about:blank should be changed");
+          aCallback();
+        });
+        return;
       }
+      // make sure the zoom level is set to 1
+      is(aWindow.ZoomManager.zoom, 1, "Zoom level for about:privatebrowsing should be reset");
 
       aCallback();
     }, true);
@@ -31,10 +33,18 @@ function test() {
 
   function finishTest() {
     // cleanup
+    let numWindows = windowsToReset.length;
+    if (!numWindows) {
+      finish();
+      return;
+    }
     windowsToReset.forEach(function(win) {
-      win.FullZoom.reset();
+      win.FullZoom.reset(function onReset() {
+        numWindows--;
+        if (!numWindows)
+          finish();
+      });
     });
-    finish();
   }
 
   function testOnWindow(options, callback) {
diff --git a/dom/interfaces/base/nsIContentPrefService2.idl b/dom/interfaces/base/nsIContentPrefService2.idl
index 4ff2434e4af7..22f8cd1714fc 100644
--- a/dom/interfaces/base/nsIContentPrefService2.idl
+++ b/dom/interfaces/base/nsIContentPrefService2.idl
@@ -59,11 +59,15 @@ interface nsIContentPref;
  *
  * Callbacks
  *
- * The methods of callback objects are always called asynchronously.  See
- * nsIContentPrefCallback2 below for more information about callbacks.
+ * The methods of callback objects are always called asynchronously.
+ *
+ * Observers are called after callbacks are called, but they are called in the
+ * same turn of the event loop as callbacks.
+ *
+ * See nsIContentPrefCallback2 below for more information about callbacks.
  */
 
-[scriptable, uuid(51e1d34a-5e9d-4b77-b14c-0f8346e264ca)]
+[scriptable, uuid(133608c7-f812-41ca-bc1c-62a4eb95e52a)]
 interface nsIContentPrefService2 : nsISupports
 {
   /**
@@ -318,6 +322,17 @@ interface nsIContentPrefService2 : nsISupports
    */
   void removeObserverForName(in AString name,
                              in nsIContentPrefObserver observer);
+
+  /**
+   * Extracts and returns the domain from the given string representation of a
+   * URI.  This is how the API extracts domains from URIs passed to it.
+   *
+   * @param str  The string representation of a URI, like
+   *             "http://example.com/foo/bar".
+   * @return     If the given string is a valid URI, the domain of that URI is
+   *             returned.  Otherwise, the string itself is returned.
+   */
+  AString extractDomain(in AString str);
 };
 
 /**
@@ -336,7 +351,7 @@ interface nsIContentPrefCallback2 : nsISupports
 
   /**
    * Called when an error occurs.  This may be called multiple times before
-   * onComplete is called.
+   * handleCompletion is called.
    *
    * @param error  A number in Components.results describing the error.
    */
diff --git a/toolkit/components/contentprefs/ContentPrefService2.jsm b/toolkit/components/contentprefs/ContentPrefService2.jsm
index 6b4085e03dca..9722fe4e5679 100644
--- a/toolkit/components/contentprefs/ContentPrefService2.jsm
+++ b/toolkit/components/contentprefs/ContentPrefService2.jsm
@@ -195,8 +195,8 @@ ContentPrefService2.prototype = {
     if (context && context.usePrivateBrowsing) {
       this._pbStore.set(group, name, value);
       this._schedule(function () {
-        this._cps._broadcastPrefSet(group, name, value);
         cbHandleCompletion(callback, Ci.nsIContentPrefCallback2.COMPLETE_OK);
+        this._cps._broadcastPrefSet(group, name, value);
       });
       return;
     }
@@ -258,11 +258,11 @@ ContentPrefService2.prototype = {
 
     this._execStmts(stmts, {
       onDone: function onDone(reason, ok) {
-        if (ok) {
+        if (ok)
           this._cache.setWithCast(group, name, value);
-          this._cps._broadcastPrefSet(group, name, value);
-        }
         cbHandleCompletion(callback, reason);
+        if (ok)
+          this._cps._broadcastPrefSet(group, name, value);
       },
       onError: function onError(nsresult) {
         cbHandleError(callback, nsresult);
@@ -342,11 +342,13 @@ ContentPrefService2.prototype = {
               this._pbStore.remove(sgroup, name);
             }
           }
+        }
+        cbHandleCompletion(callback, reason);
+        if (ok) {
           for (let [sgroup, , ] in prefs) {
             this._cps._broadcastPrefRemoved(sgroup, name);
           }
         }
-        cbHandleCompletion(callback, reason);
       },
       onError: function onError(nsresult) {
         cbHandleError(callback, nsresult);
@@ -421,18 +423,18 @@ ContentPrefService2.prototype = {
         this._cache.set(grp, name, undefined);
       },
       onDone: function onDone(reason, ok) {
-        if (ok) {
-          if (context && context.usePrivateBrowsing) {
-            for (let [sgroup, sname, ] in this._pbStore) {
-              prefs.set(sgroup, sname);
-              this._pbStore.remove(sgroup, sname);
-            }
+        if (ok && context && context.usePrivateBrowsing) {
+          for (let [sgroup, sname, ] in this._pbStore) {
+            prefs.set(sgroup, sname);
+            this._pbStore.remove(sgroup, sname);
           }
+        }
+        cbHandleCompletion(callback, reason);
+        if (ok) {
           for (let [sgroup, sname, ] in prefs) {
             this._cps._broadcastPrefRemoved(sgroup, sname);
           }
         }
-        cbHandleCompletion(callback, reason);
       },
       onError: function onError(nsresult) {
         cbHandleError(callback, nsresult);
@@ -473,18 +475,18 @@ ContentPrefService2.prototype = {
         this._cache.set(grp, name, undefined);
       },
       onDone: function onDone(reason, ok) {
-        if (ok) {
-          if (context && context.usePrivateBrowsing) {
-            for (let [sgroup, sname, ] in this._pbStore) {
-              prefs.set(sgroup, sname);
-            }
-            this._pbStore.removeGrouped();
+        if (ok && context && context.usePrivateBrowsing) {
+          for (let [sgroup, sname, ] in this._pbStore) {
+            prefs.set(sgroup, sname);
           }
+          this._pbStore.removeGrouped();
+        }
+        cbHandleCompletion(callback, reason);
+        if (ok) {
           for (let [sgroup, sname, ] in prefs) {
             this._cps._broadcastPrefRemoved(sgroup, sname);
           }
         }
-        cbHandleCompletion(callback, reason);
       },
       onError: function onError(nsresult) {
         cbHandleError(callback, nsresult);
@@ -544,20 +546,20 @@ ContentPrefService2.prototype = {
         this._cache.set(grp, name, undefined);
       },
       onDone: function onDone(reason, ok) {
-        if (ok) {
-          if (context && context.usePrivateBrowsing) {
-            for (let [sgroup, sname, ] in this._pbStore) {
-              if (sname === name) {
-                prefs.set(sgroup, name);
-                this._pbStore.remove(sgroup, name);
-              }
+        if (ok && context && context.usePrivateBrowsing) {
+          for (let [sgroup, sname, ] in this._pbStore) {
+            if (sname === name) {
+              prefs.set(sgroup, name);
+              this._pbStore.remove(sgroup, name);
             }
           }
+        }
+        cbHandleCompletion(callback, reason);
+        if (ok) {
           for (let [sgroup, , ] in prefs) {
             this._cps._broadcastPrefRemoved(sgroup, name);
           }
         }
-        cbHandleCompletion(callback, reason);
       },
       onError: function onError(nsresult) {
         cbHandleError(callback, nsresult);
@@ -682,6 +684,10 @@ ContentPrefService2.prototype = {
     this._cps.removeObserver(name, observer);
   },
 
+  extractDomain: function CPS2_extractDomain(str) {
+    return this._parseGroup(str);
+  },
+
   /**
    * Tests use this as a backchannel by calling it directly.
    *
diff --git a/toolkit/components/contentprefs/tests/unit_cps2/head.js b/toolkit/components/contentprefs/tests/unit_cps2/head.js
index ac0c45a2c86b..03e4bd4cf820 100644
--- a/toolkit/components/contentprefs/tests/unit_cps2/head.js
+++ b/toolkit/components/contentprefs/tests/unit_cps2/head.js
@@ -273,7 +273,7 @@ function dbOK(expectedRows) {
   stmt.finalize();
 }
 
-function on(event, names) {
+function on(event, names, dontRemove) {
   let args = {
     reset: function () {
       for (let prop in this) {
@@ -281,9 +281,6 @@ function on(event, names) {
           this[prop].splice(0, this[prop].length);
       }
     },
-    destroy: function () {
-      names.forEach(function (n) cps.removeObserverForName(n, observers[n]));
-    },
   };
 
   let observers = {};
@@ -302,7 +299,15 @@ function on(event, names) {
     cps.addObserverForName(name, obs);
   });
 
-  return args;
+  do_execute_soon(function () {
+    if (!dontRemove)
+      names.forEach(function (n) cps.removeObserverForName(n, observers[n]));
+    next(args);
+  });
+}
+
+function wait() {
+  do_execute_soon(next);
 }
 
 function observerArgsOK(actualArgs, expectedArgs) {
diff --git a/toolkit/components/contentprefs/tests/unit_cps2/test_extractDomain.js b/toolkit/components/contentprefs/tests/unit_cps2/test_extractDomain.js
new file mode 100644
index 000000000000..2ec3d6878b68
--- /dev/null
+++ b/toolkit/components/contentprefs/tests/unit_cps2/test_extractDomain.js
@@ -0,0 +1,20 @@
+/* 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 run_test() {
+  let tests = {
+    "http://example.com": "example.com",
+    "http://example.com/": "example.com",
+    "http://example.com/foo/bar/baz": "example.com",
+    "http://subdomain.example.com/foo/bar/baz": "subdomain.example.com",
+    "http://qix.quux.example.com/foo/bar/baz": "qix.quux.example.com",
+    "file:///home/foo/bar": "file:///home/foo/bar",
+    "not a url": "not a url",
+  };
+  let cps = Cc["@mozilla.org/content-pref/service;1"].
+            getService(Ci.nsIContentPrefService2);
+  for (let url in tests) {
+    do_check_eq(cps.extractDomain(url), tests[url]);
+  }
+}
diff --git a/toolkit/components/contentprefs/tests/unit_cps2/test_observers.js b/toolkit/components/contentprefs/tests/unit_cps2/test_observers.js
index 421d0693068f..398d4b80edb3 100644
--- a/toolkit/components/contentprefs/tests/unit_cps2/test_observers.js
+++ b/toolkit/components/contentprefs/tests/unit_cps2/test_observers.js
@@ -9,43 +9,40 @@ function run_test() {
 let tests = [
 
   function observerForName_set() {
-    let args = on("Set", ["foo", null, "bar"]);
-
     yield set("a.com", "foo", 1);
+    let args = yield on("Set", ["foo", null, "bar"]);
     observerArgsOK(args.foo, [["a.com", "foo", 1]]);
     observerArgsOK(args.null, [["a.com", "foo", 1]]);
     observerArgsOK(args.bar, []);
-    args.reset();
 
     yield setGlobal("foo", 2);
+    args = yield on("Set", ["foo", null, "bar"]);
     observerArgsOK(args.foo, [[null, "foo", 2]]);
     observerArgsOK(args.null, [[null, "foo", 2]]);
     observerArgsOK(args.bar, []);
-    args.reset();
   },
 
   function observerForName_remove() {
     yield set("a.com", "foo", 1);
     yield setGlobal("foo", 2);
 
-    let args = on("Removed", ["foo", null, "bar"]);
     yield cps.removeByDomainAndName("a.com", "bogus", null, makeCallback());
+    let args = yield on("Removed", ["foo", null, "bar"]);
     observerArgsOK(args.foo, []);
     observerArgsOK(args.null, []);
     observerArgsOK(args.bar, []);
-    args.reset();
 
     yield cps.removeByDomainAndName("a.com", "foo", null, makeCallback());
+    args = yield on("Removed", ["foo", null, "bar"]);
     observerArgsOK(args.foo, [["a.com", "foo"]]);
     observerArgsOK(args.null, [["a.com", "foo"]]);
     observerArgsOK(args.bar, []);
-    args.reset();
 
     yield cps.removeGlobal("foo", null, makeCallback());
+    args = yield on("Removed", ["foo", null, "bar"]);
     observerArgsOK(args.foo, [[null, "foo"]]);
     observerArgsOK(args.null, [[null, "foo"]]);
     observerArgsOK(args.bar, []);
-    args.reset();
   },
 
   function observerForName_removeByDomain() {
@@ -53,24 +50,23 @@ let tests = [
     yield set("b.a.com", "bar", 2);
     yield setGlobal("foo", 3);
 
-    let args = on("Removed", ["foo", null, "bar"]);
     yield cps.removeByDomain("bogus", null, makeCallback());
+    let args = yield on("Removed", ["foo", null, "bar"]);
     observerArgsOK(args.foo, []);
     observerArgsOK(args.null, []);
     observerArgsOK(args.bar, []);
-    args.reset();
 
     yield cps.removeBySubdomain("a.com", null, makeCallback());
+    args = yield on("Removed", ["foo", null, "bar"]);
     observerArgsOK(args.foo, [["a.com", "foo"]]);
     observerArgsOK(args.null, [["a.com", "foo"], ["b.a.com", "bar"]]);
     observerArgsOK(args.bar, [["b.a.com", "bar"]]);
-    args.reset();
 
     yield cps.removeAllGlobals(null, makeCallback());
+    args = yield on("Removed", ["foo", null, "bar"]);
     observerArgsOK(args.foo, [[null, "foo"]]);
     observerArgsOK(args.null, [[null, "foo"]]);
     observerArgsOK(args.bar, []);
-    args.reset();
   },
 
   function observerForName_removeAllDomains() {
@@ -78,12 +74,11 @@ let tests = [
     yield setGlobal("foo", 2);
     yield set("b.com", "bar", 3);
 
-    let args = on("Removed", ["foo", null, "bar"]);
     yield cps.removeAllDomains(null, makeCallback());
+    let args = yield on("Removed", ["foo", null, "bar"]);
     observerArgsOK(args.foo, [["a.com", "foo"]]);
     observerArgsOK(args.null, [["a.com", "foo"], ["b.com", "bar"]]);
     observerArgsOK(args.bar, [["b.com", "bar"]]);
-    args.reset();
   },
 
   function observerForName_removeByName() {
@@ -91,25 +86,25 @@ let tests = [
     yield set("a.com", "bar", 2);
     yield setGlobal("foo", 3);
 
-    let args = on("Removed", ["foo", null, "bar"]);
     yield cps.removeByName("bogus", null, makeCallback());
+    let args = yield on("Removed", ["foo", null, "bar"]);
     observerArgsOK(args.foo, []);
     observerArgsOK(args.null, []);
     observerArgsOK(args.bar, []);
-    args.reset();
 
     yield cps.removeByName("foo", null, makeCallback());
+    args = yield on("Removed", ["foo", null, "bar"]);
     observerArgsOK(args.foo, [["a.com", "foo"], [null, "foo"]]);
     observerArgsOK(args.null, [["a.com", "foo"], [null, "foo"]]);
     observerArgsOK(args.bar, []);
-    args.reset();
   },
 
   function removeObserverForName() {
-    let args = on("Set", ["foo", null, "bar"]);
+    let args = yield on("Set", ["foo", null, "bar"], true);
 
     cps.removeObserverForName("foo", args.foo.observer);
     yield set("a.com", "foo", 1);
+    yield wait();
     observerArgsOK(args.foo, []);
     observerArgsOK(args.null, [["a.com", "foo", 1]]);
     observerArgsOK(args.bar, []);
@@ -117,6 +112,7 @@ let tests = [
 
     cps.removeObserverForName(null, args.null.observer);
     yield set("a.com", "foo", 2);
+    yield wait();
     observerArgsOK(args.foo, []);
     observerArgsOK(args.null, []);
     observerArgsOK(args.bar, []);
diff --git a/toolkit/components/contentprefs/tests/unit_cps2/xpcshell.ini b/toolkit/components/contentprefs/tests/unit_cps2/xpcshell.ini
index 0fad2a9f2a94..cf1e1f5eb159 100644
--- a/toolkit/components/contentprefs/tests/unit_cps2/xpcshell.ini
+++ b/toolkit/components/contentprefs/tests/unit_cps2/xpcshell.ini
@@ -12,3 +12,4 @@ tail =
 [test_getCached.js]
 [test_getCachedSubdomains.js]
 [test_observers.js]
+[test_extractDomain.js]