diff -r 000000000000 -r 6474c204b198 toolkit/components/prompts/content/commonDialog.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/prompts/content/commonDialog.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,73 @@
+/* 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/. */
+
+const Ci = Components.interfaces;
+const Cr = Components.results;
+const Cc = Components.classes;
+const Cu = Components.utils;
+
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource://gre/modules/CommonDialog.jsm");
+
+let propBag, args, Dialog;
+
+function commonDialogOnLoad() {
+    propBag = window.arguments[0].QueryInterface(Ci.nsIWritablePropertyBag2)
+                                 .QueryInterface(Ci.nsIWritablePropertyBag);
+    // Convert to a JS object
+    args = {};
+    let propEnum = propBag.enumerator;
+    while (propEnum.hasMoreElements()) {
+        let prop = propEnum.getNext().QueryInterface(Ci.nsIProperty);
+        args[prop.name] = prop.value;
+    }
+
+    let dialog = document.documentElement;
+
+    let ui = {
+        prompt             : window,
+        loginContainer     : document.getElementById("loginContainer"),
+        loginTextbox       : document.getElementById("loginTextbox"),
+        loginLabel         : document.getElementById("loginLabel"),
+        password1Container : document.getElementById("password1Container"),
+        password1Textbox   : document.getElementById("password1Textbox"),
+        password1Label     : document.getElementById("password1Label"),
+        infoBody           : document.getElementById("info.body"),
+        infoTitle          : document.getElementById("info.title"),
+        infoIcon           : document.getElementById("info.icon"),
+        checkbox           : document.getElementById("checkbox"),
+        checkboxContainer  : document.getElementById("checkboxContainer"),
+        button3            : dialog.getButton("extra2"),
+        button2            : dialog.getButton("extra1"),
+        button1            : dialog.getButton("cancel"),
+        button0            : dialog.getButton("accept"),
+        focusTarget        : window,
+    };
+
+    // limit the dialog to the screen width
+    document.getElementById("filler").maxWidth = screen.availWidth;
+    Services.obs.addObserver(softkbObserver, "softkb-change", false);
+
+    Dialog = new CommonDialog(args, ui);
+    Dialog.onLoad(dialog);
+    window.getAttention();
+}
+
+function commonDialogOnUnload() {
+    Services.obs.removeObserver(softkbObserver, "softkb-change");
+    // Convert args back into property bag
+    for (let propName in args)
+        propBag.setProperty(propName, args[propName]);
+}
+
+function softkbObserver(subject, topic, data) {
+    let rect = JSON.parse(data);
+    if (rect) {
+        let height = rect.bottom - rect.top;
+        let width  = rect.right - rect.left;
+        let top    = (rect.top + (height - window.innerHeight) / 2);
+        let left   = (rect.left + (width - window.innerWidth) / 2);
+        window.moveTo(left, top);
+    }
+}