About the Firefox "memory leak"
 

A lot of people complain about the Firefox "memory leak(s)". All versions of Firefox no doubt leak memory - it is a common problem with software this complicated. We look to fix the issues where we can. David Baron and others have done a huge amount of excellent work in this area.

What I think many people are talking about however with Firefox 1.5 is not really a memory leak at all. It is in fact a feature.