One of the biggest pains about FF is its poor to abysmal cacheing implementation.  
Dunt get me wrong.  IE is a pain and you have to be careful to not fall into the trap of using MS proprietary things (although I do like being able to set the scrollbar colors).
I have to use FF as I do the WEB site here, and since I loaded it, I have found it to be a pain.  Had to set the cache size to 0 in order to actually see what I am doing.
I constantly get complaints from people who use FF, such as when we release a patch to the game.  They cannot see it unless they refresh the cache.