diff -r 000000000000 -r 6474c204b198 toolkit/components/startup/tests/browser/head.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/startup/tests/browser/head.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,28 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const XUL_NS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
+
+function whenBrowserLoaded(browser, callback) {
+  browser.addEventListener("load", function onLoad(event) {
+    if (event.target == browser.contentDocument) {
+      browser.removeEventListener("load", onLoad, true);
+      executeSoon(callback);
+    }
+  }, true);
+}
+
+function waitForOnBeforeUnloadDialog(browser, callback) {
+  browser.addEventListener("DOMWillOpenModalDialog", function onModalDialog() {
+    browser.removeEventListener("DOMWillOpenModalDialog", onModalDialog, true);
+
+    executeSoon(() => {
+      let stack = browser.parentNode;
+      let dialogs = stack.getElementsByTagNameNS(XUL_NS, "tabmodalprompt");
+      let {button0, button1} = dialogs[0].ui;
+      callback(button0, button1);
+    });
+  }, true);
+}