Yeah, I can reproduce this. I think it might have to do with the .page class or the fact that there are about 800 tables and FF might get flubbed upon them 🙂
But I do see it. It only happens if the table starts out expanded (i.e. running across the screen like the rest of it should), then when you click a link, it shrinks the table to be like 1/2 it's original size.
I've seen this happen when viewing topic listings via Firefox before, except I don't have to click anything, it just renders as 1/2 the width it should be.
EDIT Firefox 3 beta 2 (well, the pre-release of beta 2) seems to not have this issue.... it may be due to ad-block plus 😉