diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testStringBufferMallocAccounting.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testStringBufferMallocAccounting.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,18 @@
+// first build a big honkin' string
+str = "a";
+for (var i = 0; i < 20; ++i)
+    str = str + str;
+str.indexOf('a');
+
+var f;
+f = makeFinalizeObserver();
+assertEq(finalizeCount(), 0);
+
+// Create another observer to make sure that we overwrite all conservative
+// roots for the previous one and can observer the GC.
+f = makeFinalizeObserver();
+
+// if the assert fails, add more iterations
+for (var i = 0; i < 80; ++i)
+    str.replace(/(a)/, '$1');
+//assertEq(finalizeCount(), 1);