Firefox 1.5 was a piece of crap with memory leaks galore.
I sure hope 2.0 isn't another hunk of junk.
Those memory leaks were in all prior versions; some were actually fixed in 1.5, more fixed in 1.5.0.2. 2.x will have more fixes, but 3.x is where nearly everything has been eradicated.
Still better than Windows Internet Explorer.