Hmm, I no longer have an older installed Firefox version to compare with, but in Firefox 2.0 the font settings are at:
Firefox -> Preferences -> Content tab -> Fonts & Colors section -> Advanced button
Or, for lesser computers:
Tools -> Options -> Content tab -> Fonts & Colors section -> Advanced button
It's also worth noting that you can use cmd/ctrl key combined with '=' or '-' to increase or decrease all displayed fonts on the current tab. There's no need to be limited to what a web site chooses for you by default.