diff -r 000000000000 -r 6474c204b198 js/src/tests/js1_8_5/extensions/browser.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/js1_8_5/extensions/browser.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,6 @@
+// The page loaded in the browser is jsreftest.html, which is located in
+// js/src/tests. That makes Worker script URLs resolve relative to the wrong
+// directory. workerDir is the workaround.
+workerDir = (document.location.href.replace(/\/[^/?]*(\?.*)?$/, '/') +
+             'js1_8_5/extensions/');
+