I'm using Mozilla 1.7.12 ---- and am having the same problem.

Enter a thread, read stuff, hit back ... and nothing. No response whatsoever. The "working" indicator in top right doesn't change, no "waiting for/reading from" ... in the status line.

The only way I can get back to the forum is to go through the drop-down history , clicking each one in succession til one works..

And, yes, it was working yesterday...

Cheers,
Diolma