--- a/toolkit/content/WindowDraggingUtils.jsm
+++ b/toolkit/content/WindowDraggingUtils.jsm
@@ -45,17 +45,19 @@ function WindowDraggingElement(elem, win
 WindowDraggingElement.prototype = {
   mouseDownCheck: function(e) { return true; },
   dragTags: ["box", "hbox", "vbox", "spacer", "label", "statusbarpanel", "stack",
              "toolbaritem", "toolbarseparator", "toolbarspring", "toolbarspacer",
              "radiogroup", "deck", "scrollbox", "arrowscrollbox", "tabs"],
   handleEvent: function(aEvent) {
     switch (aEvent.type) {
       case "mousedown":
-        if (aEvent.button != 0 || !this.mouseDownCheck.call(this._elem, aEvent) ||
+        if (aEvent.button != 0 ||
+            this._window.fullScreen ||
+            !this.mouseDownCheck.call(this._elem, aEvent) ||
             aEvent.getPreventDefault())
           return;
 
         let target = aEvent.originalTarget, parent = aEvent.originalTarget;
         while (parent != this._elem) {
           let mousethrough = parent.getAttribute("mousethrough");
           if (mousethrough == "always")
             target = parent.parentNode;

--- a/toolkit/content/widgets/toolbar.xml
+++ b/toolkit/content/widgets/toolbar.xml
@@ -442,18 +442,18 @@
     <implementation>
       <constructor><![CDATA[
         if (!this._draggableStarted) {
           this._draggableStarted = true;
           try {
             Components.utils.import("resource://gre/modules/WindowDraggingUtils.jsm");
             let draggableThis = new WindowDraggingElement(this, window);
             draggableThis.mouseDownCheck = function(e) {
-              // Don't move while customizing or while in full screen mode.
-              return !this.parentNode.customizing && !window.fullScreen;
+              // Don't move while customizing.
+              return !this.parentNode.customizing;
             }
           } catch (e) {}
         }
       ]]></constructor>
     </implementation>
   </binding>
 
   <binding id="menubar" extends="chrome://global/content/bindings/toolbar.xml#toolbar-base" display="xul:menubar">