--- a/browser/base/content/browser-thumbnails.js
+++ b/browser/base/content/browser-thumbnails.js
@@ -6,16 +6,23 @@
  * Keeps thumbnails of open web pages up-to-date.
  */
 var gBrowserThumbnails = {
   /**
    * Pref that controls whether we can store SSL content on disk
    */
   PREF_DISK_CACHE_SSL: "browser.cache.disk_cache_ssl",
 
+  /**
+   * Pref that controls whether activity stream is enabled
+   */
+  PREF_ACTIVITY_STREAM_ENABLED: "browser.newtabpage.activity-stream.enabled",
+
+  _activityStreamEnabled: null,
+
   _captureDelayMS: 1000,
 
   /**
    * Used to keep track of disk_cache_ssl preference
    */
   _sslDiskCacheEnabled: null,
 
   /**
@@ -32,31 +39,36 @@ var gBrowserThumbnails = {
    * List of tab events we want to listen for.
    */
   _tabEvents: ["TabClose", "TabSelect"],
 
   init: function Thumbnails_init() {
     PageThumbs.addExpirationFilter(this);
     gBrowser.addTabsProgressListener(this);
     Services.prefs.addObserver(this.PREF_DISK_CACHE_SSL, this);
+    Services.prefs.addObserver(this.PREF_ACTIVITY_STREAM_ENABLED, this);
 
     this._sslDiskCacheEnabled =
       Services.prefs.getBoolPref(this.PREF_DISK_CACHE_SSL);
+    this._activityStreamEnabled =
+      Services.prefs.getBoolPref(this.PREF_ACTIVITY_STREAM_ENABLED);
 
     this._tabEvents.forEach(function(aEvent) {
       gBrowser.tabContainer.addEventListener(aEvent, this);
     }, this);
 
     this._timeouts = new WeakMap();
   },
 
   uninit: function Thumbnails_uninit() {
     PageThumbs.removeExpirationFilter(this);
     gBrowser.removeTabsProgressListener(this);
     Services.prefs.removeObserver(this.PREF_DISK_CACHE_SSL, this);
+    Services.prefs.removeObserver(this.PREF_ACTIVITY_STREAM_ENABLED, this);
+
     if (this._topSiteURLsRefreshTimer) {
       this._topSiteURLsRefreshTimer.cancel();
       this._topSiteURLsRefreshTimer = null;
     }
 
     this._tabEvents.forEach(function(aEvent) {
       gBrowser.tabContainer.removeEventListener(aEvent, this);
     }, this);
@@ -74,56 +86,71 @@ var gBrowserThumbnails = {
         break;
       case "TabClose": {
         this._clearTimeout(aEvent.target.linkedBrowser);
         break;
       }
     }
   },
 
-  observe: function Thumbnails_observe() {
-    this._sslDiskCacheEnabled =
-      Services.prefs.getBoolPref(this.PREF_DISK_CACHE_SSL);
+  observe: function Thumbnails_observe(subject, topic, data) {
+    switch (data) {
+      case this.PREF_DISK_CACHE_SSL:
+        this._sslDiskCacheEnabled =
+          Services.prefs.getBoolPref(this.PREF_DISK_CACHE_SSL);
+        break;
+      case this.PREF_ACTIVITY_STREAM_ENABLED:
+        this._activityStreamEnabled =
+          Services.prefs.getBoolPref(this.PREF_ACTIVITY_STREAM_ENABLED);
+        // Get the new top sites
+        XPCOMUtils.defineLazyGetter(this, "_topSiteURLs", getTopSiteURLs);
+        break;
+    }
   },
 
+  /**
+   * clearTopSiteURLCache is only ever called if we've created an nsITimer,
+   * which only happens if we've loaded the tiles top sites. Therefore we only
+   * need to clear the tiles top sites (and not activity stream's top sites)
+   */
   clearTopSiteURLCache: function Thumbnails_clearTopSiteURLCache() {
     if (this._topSiteURLsRefreshTimer) {
       this._topSiteURLsRefreshTimer.cancel();
       this._topSiteURLsRefreshTimer = null;
     }
     // Delete the defined property
     delete this._topSiteURLs;
-    XPCOMUtils.defineLazyGetter(this, "_topSiteURLs",
-                                Thumbnails_getTopSiteURLs);
+    XPCOMUtils.defineLazyGetter(this, "_topSiteURLs", getTopSiteURLs);
   },
 
   notify: function Thumbnails_notify(timer) {
     gBrowserThumbnails._topSiteURLsRefreshTimer = null;
     gBrowserThumbnails.clearTopSiteURLCache();
   },
 
-  filterForThumbnailExpiration:
-  function Thumbnails_filterForThumbnailExpiration(aCallback) {
-    aCallback(this._topSiteURLs);
+  async filterForThumbnailExpiration(aCallback) {
+    const topSites = await this._topSiteURLs;
+    aCallback(topSites);
   },
 
   /**
    * State change progress listener for all tabs.
    */
   onStateChange: function Thumbnails_onStateChange(aBrowser, aWebProgress,
                                                    aRequest, aStateFlags, aStatus) {
     if (aStateFlags & Ci.nsIWebProgressListener.STATE_STOP &&
         aStateFlags & Ci.nsIWebProgressListener.STATE_IS_NETWORK)
       this._delayedCapture(aBrowser);
   },
 
-  _capture: function Thumbnails_capture(aBrowser) {
+  async _capture(aBrowser) {
     // Only capture about:newtab top sites.
+    const topSites = await this._topSiteURLs;
     if (!aBrowser.currentURI ||
-        this._topSiteURLs.indexOf(aBrowser.currentURI.spec) == -1)
+        topSites.indexOf(aBrowser.currentURI.spec) == -1)
       return;
     this._shouldCapture(aBrowser, function(aResult) {
       if (aResult) {
         PageThumbs.captureAndStoreIfStale(aBrowser);
       }
     });
   },
 
@@ -154,26 +181,30 @@ var gBrowserThumbnails = {
     if (this._timeouts.has(aBrowser)) {
       aBrowser.removeEventListener("scroll", this);
       clearTimeout(this._timeouts.get(aBrowser));
       this._timeouts.delete(aBrowser);
     }
   }
 };
 
-function Thumbnails_getTopSiteURLs() {
-  // The _topSiteURLs getter can be expensive to run, but its return value can
-  // change frequently on new profiles, so as a compromise we cache its return
-  // value as a lazy getter for 1 minute every time it's called.
-  gBrowserThumbnails._topSiteURLsRefreshTimer =
-    Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
-  gBrowserThumbnails._topSiteURLsRefreshTimer.initWithCallback(gBrowserThumbnails,
-                                                               60 * 1000,
-                                                               Ci.nsITimer.TYPE_ONE_SHOT);
-  return NewTabUtils.links.getLinks().reduce((urls, link) => {
-    if (link)
-      urls.push(link.url);
+async function getTopSiteURLs() {
+  let sites = [];
+  if (gBrowserThumbnails._activityStreamEnabled) {
+    sites = await NewTabUtils.activityStreamLinks.getTopSites();
+  } else {
+    // The _topSiteURLs getter can be expensive to run, but its return value can
+    // change frequently on new profiles, so as a compromise we cache its return
+    // value as a lazy getter for 1 minute every time it's called.
+    gBrowserThumbnails._topSiteURLsRefreshTimer =
+      Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
+    gBrowserThumbnails._topSiteURLsRefreshTimer.initWithCallback(gBrowserThumbnails,
+                                                                 60 * 1000,
+                                                                 Ci.nsITimer.TYPE_ONE_SHOT);
+    sites = NewTabUtils.links.getLinks();
+  }
+  return sites.reduce((urls, link) => {
+    if (link) urls.push(link.url);
     return urls;
   }, []);
 }
 
-XPCOMUtils.defineLazyGetter(gBrowserThumbnails, "_topSiteURLs",
-                            Thumbnails_getTopSiteURLs);
+XPCOMUtils.defineLazyGetter(gBrowserThumbnails, "_topSiteURLs", getTopSiteURLs);