Well I know that FF has tended to have memory leak problems but this has frequently been with badly written plugins and add-ons.

I cannot say that I have personally had any problems myself, but I have plenty of RAM

I think that it has had problems with Java as well?

Also IIRC FireFox is designed to use more RAM on systems that have it available?

The main problems that I have experienced with FF have been with performance and stability of some versions of 3.x................ like a browser shouldn't take over 5 minutes to load?

I am currently using 3.6.10 and haven't had any problems so far.