If you are absolutely sure you have tried both the suggestions in the FAQ, try using Safari.
Why? Firstly, if that works, you can avoid those timeouts.
Secondly, whether it works or not, it will provide a clue as to what is going on. If Safari also fails, it could be that a cache somewhere upstream of your computer is corrupted: you might need to talk to your ISP, but first try rebooting the Mac. If Safari works, you have a problem with Firefox and might need to try looking for a Firefox support forum.