I may have found a solution to this problem here (well, at least Firefox has been working again for the last few hours, not sure if it will prove to be a long term solution or not).

As it says in the linked article, type about:config into the address bar, find network.http.max-connections and change its value from 256 to 48.

I have absolutely no idea why this works but it seems to. According to my resource monitor Firefox still seems to be using a ridiculous amount of memory and disk, and my cpu fan is still going crazy, but at least websites are loading again!

Does this fix the problem for anyone else?

I reduced max-connections to 48, this indeed improves the loading speed but FF 7.01 is still slower than FF6 Using Win 7 SP1, Intel 8600 3.33 GHz , 4 GB mem

Have had terrible problems with running firefox for the last month or so with slow page loading and frequent hang ups.It got so bad I loaded Opera but much prefer firefox overall. Tried this fix today as above - " type about:config into the address bar, find network.http.max-connections and change its value from 256 to 48" - and it has solved all my problems. It is now going really well and have had no crashes. Thank you very much.