Need help with Firefox display problem

You have all your divs set individually on the page. Normally you enclose them in a wrapper div for better control.

you have set margins for the google ads that effectively are giving them priority for their positioning, and they are forcing the main content section and the other divs down the page when the page resizes (their fixed width doesn't help, but you have no choice in that of course).

Re-design the div layout.
Create a wrapper div to hold all the other divs, and set min-width and max-widths for better control.
Put the google ad divs inside that and just float them left and right.
then add your main content and other divs inside the wrapper as well. The wrapper div should be set with a min-width which equals the wide of the two google ad div, plus the content width, plus a bit for luck (rounding off errors mean you shouldn't go for an exact fit!)

And check that it all works okay at 800x600, because many people do not run their browser full screen, and your pages demand at least 1024 width to work. Left and right google ads are constricting how much space you have left for your content, perhaps a two column design would be better. I use just two columns on my site which has google ads (in siggy).

Hope this helps.