Only installed Firefox 2 yesterday and already I have found some quirks with it.
Go to Google do a search on anything you like, I was searching for and try and hover the mouse over the sponsored links. The first link in the list seems to be OK but the others become inaccessible to mouse users! Occasionally a few of the others seem to be OK.
I wonder if Google know about this!
Update I have tracked it down to position:relative on class g. Not sure why it is there and the page seems to render fine without it!