Make sure you get the latest version of FireFox. The problems you're describing are the same as what I'm running into with the older versions.
The fun thing is that the auto-update feature isn't going to bring you to the newest version...you have to download the full version from the site directly and install it.
Or as I'm discovering, Google's Chrome is pretty stable, quick and has some wonderful features that I'm really starting to enjoy. And unlike some other new browsers, I've yet to find a site that it wouldn't work on.