... but I still got the disjointed FF button and tabs (on top) when FF maximized, ie not exactly aligned. Might (just a guess) be a matter of whether you use a personas skin or a "classic" skin, or a matter of screen resolution.... yeah that's most likely after all.
ps: on a side note, very few classic skins are available for FF4, as they got to work with both old and new UI style, and the only available ones are absolutely ugly.