Is your code valid?
Can you post a URL?
Works fine here on Win 7. Don't have a Mac to test on sorry.
I don't know any specific problems with FF 3.6.3 but I know how problematic span tags sometimes can be. Try to re-write some partions of your code or if you're making any width/height adjustments, dont forget the display:block like i sometimes do
Hope it helps!
Do you have any examples of pages where <span> tags are problematic?
I'm just curious to see what issues you're alluding to. I've never seen any problems with them but that doesn't mean they don't exist.