All I know is that Firefox loads its upgrades automatically. But my pc is on windows xp3, maybe the recent softwares have some compatibility problem with the "old" systems.
Thunderbird gives me fits too, acting like Firefox with stacking unneeded memory. When Firefox turns dumb, usually Thunderbird too. Hard shutting Firefox (and retrieving plenty of memory) gives me back the hand on my pc, but not on Thunderbird which stays lost (and frost) and I have to hard shut it too. Then, reopening both and it's fine.
A little annoying...