it's true that some sites don't serve properly to FF because they're coded out of spec and geared towards IE. best thing to do is drop an email to the webmaster and request WWWC compliance (citing the ever increasing popularity of FF is a good thing as well). IEView is also a handy extension that I use.

i also use Tweak Network settings extension which handles many of the tweaks available in about:config (typed in address bar) that would otherwise have to be done manually (Sexy_Southerner has a post detailing these tweaks).