--- a/testing/specialpowers/content/specialpowersAPI.js
+++ b/testing/specialpowers/content/specialpowersAPI.js
@@ -2,16 +2,18 @@
  * 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/. */
 /* This code is loaded in every child process that is started by mochitest in
  * order to be used as a replacement for UniversalXPConnect
  */
 
 "use strict";
 
+var global = this;
+
 var Ci = Components.interfaces;
 var Cc = Components.classes;
 var Cu = Components.utils;
 
 Cu.import("chrome://specialpowers/content/MockFilePicker.jsm");
 Cu.import("chrome://specialpowers/content/MockColorPicker.jsm");
 Cu.import("chrome://specialpowers/content/MockPermissionPrompt.jsm");
 Cu.import("resource://gre/modules/Services.jsm");
@@ -1619,17 +1621,29 @@ SpecialPowersAPI.prototype = {
     return this.focusManager.focusedWindow;
   },
 
   focus: function(aWindow) {
     // This is called inside TestRunner._makeIframe without aWindow, because of assertions in oop mochitests
     // With aWindow, it is called in SimpleTest.waitForFocus to allow popup window opener focus switching
     if (aWindow)
       aWindow.focus();
-    sendAsyncMessage("SpecialPowers.Focus", {});
+    var mm = global;
+    if (aWindow) {
+      try {
+        mm = aWindow.QueryInterface(Ci.nsIInterfaceRequestor)
+                                    .getInterface(Ci.nsIDocShell)
+                                    .QueryInterface(Ci.nsIInterfaceRequestor)
+                                    .getInterface(Ci.nsIContentFrameMessageManager);
+      } catch (ex) {
+        /* Ignore exceptions for e.g. XUL chrome windows from mochitest-chrome
+         * which won't have a message manager */
+      }
+    }
+    mm.sendAsyncMessage("SpecialPowers.Focus", {});
   },
 
   getClipboardData: function(flavor, whichClipboard) {
     if (this._cb == null)
       this._cb = Components.classes["@mozilla.org/widget/clipboard;1"].
                             getService(Components.interfaces.nsIClipboard);
     if (whichClipboard === undefined)
       whichClipboard = this._cb.kGlobalClipboard;