diff -r 000000000000 -r 6474c204b198 xpcom/string/src/nsTStringComparator.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/string/src/nsTStringComparator.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,42 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* 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/. */
+
+int NS_FASTCALL
+Compare( const nsTSubstring_CharT::base_string_type& lhs, const nsTSubstring_CharT::base_string_type& rhs, const nsTStringComparator_CharT& comp )
+  {
+    typedef nsTSubstring_CharT::size_type size_type;
+
+    if ( &lhs == &rhs )
+      return 0;
+
+    nsTSubstring_CharT::const_iterator leftIter, rightIter;
+    lhs.BeginReading(leftIter);
+    rhs.BeginReading(rightIter);
+
+    size_type lLength = leftIter.size_forward();
+    size_type rLength = rightIter.size_forward();
+    size_type lengthToCompare = XPCOM_MIN(lLength, rLength);
+
+    int result;
+    if ( (result = comp(leftIter.get(), rightIter.get(), lengthToCompare, lengthToCompare)) == 0 )
+      {
+        if ( lLength < rLength )
+          result = -1;
+        else if ( rLength < lLength )
+          result = 1;
+        else
+          result = 0;
+      }
+
+    return result;
+  }
+
+int
+nsTDefaultStringComparator_CharT::operator()( const char_type* lhs, const char_type* rhs, uint32_t lLength, uint32_t rLength) const
+  {
+    return (lLength == rLength) ? nsCharTraits<CharT>::compare(lhs, rhs, lLength) :
+           (lLength > rLength) ? 1 : -1;
+  }