mmm I think it may be your computer. I'm good, but I'm not that good to get it to do that on only your computer
Clean your cache. Something has been corrupted.
Does it do that with another browser or just Firefox?
Thinking about it, all your problems seems to be Javascript related. Nothing has changed with the forum. So have a look if you've installed any firefox extensions, popup blockers, or firefox extensions that could be effecting the way the forum behaves.