diff -r 000000000000 -r 6474c204b198 content/base/src/nsAttrValueOrString.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/content/base/src/nsAttrValueOrString.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,24 @@
+/* -*- 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/. */
+
+#include "nsAttrValueOrString.h"
+
+const nsAString&
+nsAttrValueOrString::String() const
+{
+  if (mStringPtr) {
+    return *mStringPtr;
+  }
+
+  if (mAttrValue->Type() == nsAttrValue::eString) {
+    mCheapString = mAttrValue->GetStringValue();
+    mStringPtr = &mCheapString;
+    return *mStringPtr;
+  }
+
+  mAttrValue->ToString(mCheapString);
+  mStringPtr = &mCheapString;
+  return *mStringPtr;
+}