jemalloc, the new default memory allocator in FreeBSD and set to become the internal allocator in Firefox 3, was turned on by default for Linux today. That means by tonight Linux builds should go live on the aforementioned nightlies page with jemalloc enabled. The reason we are integrating our own allocator is that we’ve found jemalloc to be better than all the default allocators of our three main platforms (Windows, Mac OS X and Linux). Not only is it faster (and it shows in Javascript tests!) but it causes less fragmentation, so you should see a significant memory reduction after using Firefox for a lengthy period of time.

Source:  ventnorsblog