Paula, this is probably a stupid question because I confess to knowing absolutely nothing about computers, but have you done a complete scan for a virus?   Although we use AOL we also had Firefox and up until recently everything was going fine.  Then I too started to have trouble getting onto the Forum (and only the forum) and it was only during our regular weekly in-depth scan that the OH discovered that a Trojan virus had somehow attached itself and was causing innumerable problems.  Unfortunately we also had a couple of other problems which meant we ended up having to ditch everything and take the computer back to it's original factory settings as well as getting some outside help.  My OH opted to ditch Firefox, suspecting that it might have something to do with the problem, and having re-loaded everything, we are now up and running without any problems  (Excuse me while I dash to touch a piece of wood!)  I am not saying that this is what is causing your problem, but I have noticed that a few people on the internet are experiencing problems with Firefox because their computer is under "attack" by Ad-ware and re-direct Viruses.  It's just a thought!
Margaret x