diff -r 000000000000 -r 6474c204b198 browser/base/content/sync/customize.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/base/content/sync/customize.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,25 @@
+/* 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/. */
+
+"use strict";
+
+const {classes: Cc, interfaces: Ci, utils: Cu} = Components;
+
+Cu.import("resource://gre/modules/Services.jsm");
+
+let service = Cc["@mozilla.org/weave/service;1"]
+                .getService(Ci.nsISupports)
+                .wrappedJSObject;
+
+if (!service.allowPasswordsEngine) {
+  let checkbox = document.getElementById("fxa-pweng-chk");
+  checkbox.checked = false;
+  checkbox.disabled = true;
+}
+
+addEventListener("dialogaccept", function () {
+  let pane = document.getElementById("sync-customize-pane");
+  pane.writePreferences(true);
+  window.arguments[0].accepted = true;
+});