diff -r 000000000000 -r 6474c204b198 js/src/tests/js1_5/Function/regress-178389.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/js1_5/Function/regress-178389.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,26 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+//-----------------------------------------------------------------------------
+var BUGNUMBER = 178389;
+var summary = 'Function.prototype.toSource should not override Function.prototype.toString';
+var actual = '';
+var expect = '';
+
+printBugNumber(BUGNUMBER);
+printStatus (summary);
+ 
+function f()
+{
+  var g = function (){};
+}
+
+expect = f.toString();
+
+Function.prototype.toSource = function () { return ''; };
+
+actual = f.toString();
+
+reportCompare(expect, actual, summary);