diff -r 000000000000 -r 6474c204b198 layout/tools/reftest/b2g_start_script.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/tools/reftest/b2g_start_script.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,44 @@
+/* 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 setDefaultPrefs() {
+    // This code sets the preferences for extension-based reftest.
+    var prefs = Cc["@mozilla.org/preferences-service;1"].
+                getService(Ci.nsIPrefService);
+    var branch = prefs.getDefaultBranch("");
+
+#include reftest-preferences.js
+}
+
+function setPermissions() {
+  if (__marionetteParams.length < 2) {
+    return;
+  }
+
+  let serverAddr = __marionetteParams[0];
+  let serverPort = __marionetteParams[1];
+  let perms = Cc["@mozilla.org/permissionmanager;1"]
+              .getService(Ci.nsIPermissionManager);
+  let ioService = Cc["@mozilla.org/network/io-service;1"]
+                  .getService(Ci.nsIIOService);
+  let uri = ioService.newURI("http://" + serverAddr + ":" + serverPort, null, null);
+  perms.add(uri, "allowXULXBL", Ci.nsIPermissionManager.ALLOW_ACTION);
+}
+
+// Load into any existing windows
+let wm = Cc["@mozilla.org/appshell/window-mediator;1"]
+            .getService(Ci.nsIWindowMediator);
+let win = wm.getMostRecentWindow('');
+
+// Set preferences and permissions
+setDefaultPrefs();
+setPermissions();
+
+// Loading this into the global namespace causes intermittent failures.
+// See bug 882888 for more details.
+let reftest = {};
+Cu.import("chrome://reftest/content/reftest.jsm", reftest);
+
+// Start the reftests
+reftest.OnRefTestLoad(win);