diff --git a/common/content/events.js b/common/content/events.js
index f2001ddb..0e20bb87 100644
--- a/common/content/events.js
+++ b/common/content/events.js
@@ -143,7 +143,7 @@ var Events = Module("events", {
                         this.active.push(elem);
                 }
 
-                this.active = this.active.filter(function (e) e.popupBoxObject.popupState != "closed");
+                this.active = this.active.filter(function (e) e.popupBoxObject && e.popupBoxObject.popupState != "closed");
 
                 if (!this.active.length && !this.activeMenubar)
                     modes.remove(modes.MENU, true);
diff --git a/common/modules/dom.jsm b/common/modules/dom.jsm
index 451fa60b..903a4133 100644
--- a/common/modules/dom.jsm
+++ b/common/modules/dom.jsm
@@ -803,13 +803,32 @@ var DOM = Class("DOM", {
         if (isObject(event))
             capture = listener;
         else
-            event = array.toObject([[key, val]]);
+            event = array.toObject([[event, listener]]);
 
         return this.each(function (elem) {
             for (let [k, v] in Iterator(event))
                 elem.removeEventListener(k, v.wrapper || v, capture);
         });
     },
+    once: function once(event, listener, capture) {
+        if (isObject(event))
+            capture = listener;
+        else
+            event = array.toObject([[event, listener]]);
+
+        for (let pair in Iterator(event)) {
+            let [evt, callback] = pair;
+            event[evt] = util.wrapCallback(function wrapper(event) {
+                this.removeEventListener(evt, wrapper.wrapper, capture);
+                return callback.apply(this, arguments);
+            }, true);
+        }
+
+        return this.each(function (elem) {
+            for (let [k, v] in Iterator(event))
+                elem.addEventListener(k, v, capture);
+        });
+    },
 
     dispatch: function dispatch(event, params, extraProps) {
         this.canceled = false;
diff --git a/common/modules/javascript.jsm b/common/modules/javascript.jsm
index a4d1ab6b..3cd1100d 100644
--- a/common/modules/javascript.jsm
+++ b/common/modules/javascript.jsm
@@ -55,7 +55,7 @@ var JavaScript = Module("javascript", {
 
     newContext: function () this.modules.newContext(this.modules.userContext, true),
 
-    get completers() JavaScript.completers, // For backward compatibility
+    completers: Class.Memoize(function () Object.create(JavaScript.completers)),
 
     // Some object members are only accessible as function calls
     getKey: function (obj, key) {
@@ -550,7 +550,7 @@ var JavaScript = Module("javascript", {
                 }
                 catch (e) {}
                 if (!completer)
-                    completer = JavaScript.completers[funcName];
+                    completer = this.completers[funcName];
                 if (!completer)
                     return null;
 
diff --git a/common/modules/util.jsm b/common/modules/util.jsm
index 9cc4a49e..9385bda0 100644
--- a/common/modules/util.jsm
+++ b/common/modules/util.jsm
@@ -710,6 +710,8 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
      *    responseType: {string} Override the type of the "response"
      *                  property.
      *
+     *    headers: {objects} Extra request headers.
+     *
      *    user: {string} The user name to send via HTTP Authentication.
      *    pass: {string} The password to send via HTTP Authentication.
      *
@@ -749,12 +751,18 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
                 params.data = data;
             }
 
-
             if (params.mimeType)
                 xmlhttp.overrideMimeType(params.mimeType);
 
-            xmlhttp.open(params.method || "GET", url, async,
-                         params.user, params.pass);
+            let args = [params.method || "GET", url, async];
+            if (params.user != null || params.pass != null)
+                args.push(params.user);
+            if (params.pass != null)
+                args.push(prams.pass);
+            xmlhttp.open.apply(xmlhttp, args);
+
+            for (let [header, val] in Iterator(params.headers || {}))
+                xmlhttp.setRequestHeader(header, val);
 
             if (params.responseType)
                 xmlhttp.responseType = params.responseType;