I had this problem with firefox 1.0 in SuSE 9.1 and I'm having the same problem with Slackware 10. When I open firefox, it opens in a window that has about 2-3mm of space to the right of the window. I have to maximize it to get it to take up the entire screen.
In SuSE I downgraded to 0.8 but I'd rather just fix it and stick with 1.0.
Any suggestions?

edit the command that starts firefox (menu, link, whatever, depends on the window manager you are using) make it something like this in the app execute area

firefox -g 640x480+0+0 (launches at a size 640pixels by 480 pixels, starting from the upper left corner of the screen, or fullscreen at 640x480)

edit, depending on your window manager, you can size it the way you like, click on the title bar (or alt+f3, depending) and choose advanced: remember window settings. you can also do kewl things like remeove the title bars to make a cleaner window, or in my favorite case, make rxvt run in the root window over the background, transparently

Thank you. Thank you very much (as Elvis Presley used to say).
It worked like a charm.

glad i could help