diff -r 000000000000 -r 6474c204b198 js/ductwork/debugger/tests/head_dbg.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/ductwork/debugger/tests/head_dbg.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,17 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const Cu = Components.utils;
+const Cr = Components.results;
+
+function testGlobal(aName) {
+  let systemPrincipal = Cc["@mozilla.org/systemprincipal;1"]
+    .createInstance(Ci.nsIPrincipal);
+
+  let sandbox = Cu.Sandbox(systemPrincipal);
+  Cu.evalInSandbox("this.__name = '" + aName + "'", sandbox);
+  return sandbox;
+}