I have also experienced problems with firefox lately, it goes into perputal downloading when I try to open a .pdf, but IE works OK. I know this doesn't help but, look forward to seeing if you get any answers.
I am having the same problem with this site starting about one month ago with firefox 3.0.3. When it does lock up it does show something to do with chat. As this is a new XP PC I didn't say anything as I am still tweaking it to get it to run like I want it.
If I exit the site and say to keep my tabs for next time I can come back in and continue on without any problem