Have disabled all of my add-ons, restarted Firefox 4.0, enabled the add-ons to restart Firefox 4.0 once again - the issue however persists (even after installing the latest release, Noia Hack v5.1)
Something that I noticed which might interest you is that the gray area on the left-hand-side of the 'Add-on bar' which refuses to get skinned is actually nothing but a 'Flexible Space' that is removable employing the drag-n-drop method. You may check this statement by right-clicking any empty space on the tool-bar and then clicking on 'Customize...' The stubborn 'Addon-bar' (for now) continues to look as follows:-
Have also come across other bugs which I'll post later on.
Please check my previous comments, too.
Chew Internet Explorer