diff --git a/toolkit/mozapps/extensions/content/extensions-content.js b/toolkit/mozapps/extensions/content/extensions-content.js
index b947c52fd5b..ae891eaea22 100644
--- a/toolkit/mozapps/extensions/content/extensions-content.js
+++ b/toolkit/mozapps/extensions/content/extensions-content.js
@@ -229,13 +229,24 @@ InstallTriggerManager.prototype = {
   },
 
   createInstallTrigger: function createInstallTrigger() {
-    // 'this' is the window itself. We do this in a getter, so that
-    // we create these objects only on demand (this is a potential
-    // concern, since otherwise we might add one per iframe, and
-    // keep them alive for as long as the tab is alive).
-    delete this.InstallTrigger; // remove getter
-    this.InstallTrigger = new InstallTrigger(this);
-    return this.InstallTrigger;
+    // We do this in a getter, so that we create these objects
+    // only on demand (this is a potential concern, since
+    // otherwise we might add one per iframe, and keep them
+    // alive for as long as the tab is alive).
+    // In order for this lazy instantiation to work, we need
+    // 'this' to be a window. However, we can get here with the
+    // window being on the prototype chain of our actual 'this'
+    // object (see bug 609794). Note that we need the
+    // XPCNativeWrapper.unwrap because getting the prototype
+    // doesn't respect the .wrappedJSObject unwrapping above.
+    var obj = this;
+    while (!obj.hasOwnProperty('InstallTrigger')) {
+      obj = XPCNativeWrapper.unwrap(Object.getPrototypeOf(obj));
+    }
+
+    delete obj.InstallTrigger; // remove getter
+    obj.InstallTrigger = new InstallTrigger(this);
+    return obj.InstallTrigger;
   },
 
   /**
diff --git a/toolkit/mozapps/extensions/test/Makefile.in b/toolkit/mozapps/extensions/test/Makefile.in
index 6b71abc1a72..671c1c0bcb5 100644
--- a/toolkit/mozapps/extensions/test/Makefile.in
+++ b/toolkit/mozapps/extensions/test/Makefile.in
@@ -53,6 +53,7 @@ ifneq (mobile,$(MOZ_BUILD_APP))
  DIRS +=  \
     xpinstall \
     browser \
+    mochitest \
     $(NULL)
 endif
 
diff --git a/toolkit/mozapps/extensions/test/mochitest/Makefile.in b/toolkit/mozapps/extensions/test/mochitest/Makefile.in
new file mode 100644
index 00000000000..3476b63e988
--- /dev/null
+++ b/toolkit/mozapps/extensions/test/mochitest/Makefile.in
@@ -0,0 +1,51 @@
+#
+# ***** BEGIN LICENSE BLOCK *****
+# Version: MPL 1.1/GPL 2.0/LGPL 2.1
+#
+# The contents of this file are subject to the Mozilla Public License Version
+# 1.1 (the "License"); you may not use this file except in compliance with
+# the License. You may obtain a copy of the License at
+# http://www.mozilla.org/MPL/
+#
+# Software distributed under the License is distributed on an "AS IS" basis,
+# WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+# for the specific language governing rights and limitations under the
+# License.
+#
+# The Original Code is mozilla.org code.
+#
+# The Initial Developer of the Original Code is
+# Mozilla Foundation.
+# Portions created by the Initial Developer are Copyright (C) 2007
+# the Initial Developer. All Rights Reserved.
+#
+# Contributor(s):
+#
+# Alternatively, the contents of this file may be used under the terms of
+# either of the GNU General Public License Version 2 or later (the "GPL"),
+# or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+# in which case the provisions of the GPL or the LGPL are applicable instead
+# of those above. If you wish to allow use of your version of this file only
+# under the terms of either the GPL or the LGPL, and not to allow others to
+# use your version of this file under the terms of the MPL, indicate your
+# decision by deleting the provisions above and replace them with the notice
+# and other provisions required by the GPL or the LGPL. If you do not delete
+# the provisions above, a recipient may use your version of this file under
+# the terms of any one of the MPL, the GPL or the LGPL.
+#
+# ***** END LICENSE BLOCK *****
+
+DEPTH		= ../../../../..
+topsrcdir	= @top_srcdir@
+srcdir		= @srcdir@
+VPATH		= @srcdir@
+relativesrcdir  = toolkit/mozapps/extensions/test/mochitest
+
+include $(DEPTH)/config/autoconf.mk
+include $(topsrcdir)/config/rules.mk
+
+_TEST_FILES =	test_bug609794.html \
+		$(NULL)
+
+libs:: $(_TEST_FILES)
+	$(INSTALL) $^ $(DEPTH)/_tests/testing/mochitest/tests/$(relativesrcdir)
diff --git a/toolkit/mozapps/extensions/test/mochitest/test_bug609794.html b/toolkit/mozapps/extensions/test/mochitest/test_bug609794.html
new file mode 100644
index 00000000000..2715839da9e
--- /dev/null
+++ b/toolkit/mozapps/extensions/test/mochitest/test_bug609794.html
@@ -0,0 +1,28 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=609794
+-->
+<head>
+  <title>Test for Bug 609794</title>
+  <script type="application/javascript" src="/MochiKit/packed.js"></script>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=609794">Mozilla Bug 609794</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 609794 **/
+var obj = Object.create(window);
+is(obj.InstallTrigger.toString(), "[object Object]", "can get InstallTrigger through the prototype");
+
+</script>
+</pre>
+</body>
+</html>