For a while i was "suffering" from the firefox 2 fonts looking differently from my gtk theme.
I think that's quite usual problem. The most annoying thing were the fonts, they were two steps bigger than my gtk ones.
Solution is fairly easy. Edit your firefox Chromeuser profile:
first create userChrome.css file by copying the example:
$ cd ~/.mozilla/firefox/*.default/chrome
$ cp userChrome-example.css userChrome.css
Then just edit userChrome.css and paste these lines (based on my example):
font-family: Sans-Serif !important;
font-size: 11px !important;
that will not force firefox follow your gtk settings, but will make it look the same.