diff -r 000000000000 -r 6474c204b198 js/src/builtin/Number.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/builtin/Number.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,40 @@
+/* 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/. */
+
+/*global intl_NumberFormat: false, */
+
+
+var numberFormatCache = new Record();
+
+
+/**
+ * Format this Number object into a string, using the locale and formatting options
+ * provided.
+ *
+ * Spec: ECMAScript Language Specification, 5.1 edition, 15.7.4.3.
+ * Spec: ECMAScript Internationalization API Specification, 13.2.1.
+ */
+function Number_toLocaleString() {
+    // Steps 1-2.  Note that valueOf enforces "this Number value" restrictions.
+    var x = callFunction(std_Number_valueOf, this);
+
+    // Steps 2-3.
+    var locales = arguments.length > 0 ? arguments[0] : undefined;
+    var options = arguments.length > 1 ? arguments[1] : undefined;
+
+    // Step 4.
+    var numberFormat;
+    if (locales === undefined && options === undefined) {
+        // This cache only optimizes for the old ES5 toLocaleString without
+        // locales and options.
+        if (numberFormatCache.numberFormat === undefined)
+            numberFormatCache.numberFormat = intl_NumberFormat(locales, options);
+        numberFormat = numberFormatCache.numberFormat;
+    } else {
+        numberFormat = intl_NumberFormat(locales, options);
+    }
+
+    // Step 5.
+    return intl_FormatNumber(numberFormat, x);
+}