I believe the small fonts in Firefox is a known quirk with Fedora 8 (you're using 8, I assume?). Several people on the forums have reported the problem.
Maybe this will be of some assistance:
If you really want Firefox to render pages more like they would look in Windows, you could also try installing MS TrueType fonts. Google around or search the forums.
(Also, Fedora is not = Linux. This problem with Firefox font size is not seen in all Linux distros. That's why it's a bit curious when you say "my Linux.")