diff -r 000000000000 -r 6474c204b198 toolkit/mozapps/installer/js-compare-ast.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/mozapps/installer/js-compare-ast.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,28 @@
+/* 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 script compares the AST of two JavaScript files passed as arguments.
+ * The script exits with a 0 status code if both files parse properly and the
+ * ASTs of both files are identical modulo location differences. The script
+ * exits with status code 1 if any of these conditions don't hold.
+ *
+ * This script is used as part of packaging to verify minified JavaScript files
+ * are identical to their original files.
+ */
+
+"use strict";
+
+function ast(filename) {
+  return JSON.stringify(Reflect.parse(snarf(filename), {loc: 0}));
+}
+
+if (scriptArgs.length !== 2) {
+  throw "usage: js js-compare-ast.js FILE1.js FILE2.js";
+}
+
+let ast0 = ast(scriptArgs[0]);
+let ast1 = ast(scriptArgs[1]);
+
+quit(ast0 == ast1 ? 0 : 1);