diff -r 000000000000 -r 6474c204b198 js/src/tests/js1_5/Regress/regress-315974.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/js1_5/Regress/regress-315974.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,50 @@
+/* -*- 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/. */
+
+//-----------------------------------------------------------------------------
+
+/*
+  This test case uses String.quote(), because that method uses the JS printf()
+  functions internally. The printf() functions print to a char* buffer, causing
+  conversion to and from UTF-8 if UTF-8 is enabled. If not, UTF-8 sequences are
+  converted to ASCII \uXXXX sequences. Thus, both return values are acceptable.
+*/
+
+var BUGNUMBER = 315974;
+var summary = 'Test internal printf() for wide characters';
+
+printBugNumber(BUGNUMBER);
+printStatus (summary);
+
+enterFunc (String (BUGNUMBER));
+
+var goodSurrogatePair = '\uD841\uDC42';
+var badSurrogatePair = '\uD841badbad';
+
+var goodSurrogatePairQuotedUtf8 = '"\uD841\uDC42"';
+var badSurrogatePairQuotedUtf8 = 'no error thrown!';
+var goodSurrogatePairQuotedNoUtf8 = '"\\uD841\\uDC42"';
+var badSurrogatePairQuotedNoUtf8 = '"\\uD841badbad"';
+
+var status = summary + ': String.quote() should pay respect to surrogate pairs';
+var actual = goodSurrogatePair.quote();
+/* Result in case UTF-8 is enabled. */
+var expect = goodSurrogatePairQuotedUtf8;
+/* Result in case UTF-8 is disabled. */
+if (actual != expect && actual == goodSurrogatePairQuotedNoUtf8)
+  expect = actual;
+reportCompare(expect, actual, status);
+
+/*
+ * A malformed surrogate pair throws an out-of-memory error,
+ * but only if UTF-8 is enabled.
+ */
+status = summary + ': String.quote() should throw error on bad surrogate pair';
+/* Out of memory is not catchable. */
+actual = badSurrogatePair.quote();
+/* Come here only if UTF-8 is disabled. */
+reportCompare(badSurrogatePairQuotedNoUtf8, actual, status);
+
+exitFunc (String (BUGNUMBER));