Adam, I use Firefox (1.0 Preview) and now I haven’t any problem with it. But I’ve had the same problem, as you have, before. Could read Forums, but sometimes (it was strange) I couldn’t login to post.
I couldn’t say what I did, but now I’m OK. Sometimes it asks for login, but it logs immediately and without problems. If I remeber correctly last thing I did (and after it I think it started to work) was in Privacy option (Tools-Options-Privacy); I deleted all Saved passwords, all Cookies and cleared Cache. Restarted Firefox and from that moment I’ve been without problem. But, of course, I couldn’t be really sure, if these things helped. But you can try.
Oh, one more thing. I was on older Firefox version (0.9.. something) and maybe new version helped me out of this (speaking of 1.0 Preview).
But now it's time to be gone - forever...