There are still major issues. I haven’t had any stability problems, but there are bad memory leaks. Gran Paradiso, as Firefox 3 is code named, launches using about 33mb of RAM; after ten minutes of browsing that number jumped to 100mb and after a couple of hours it was close to 400mb — and that’s with no extensions installed.
It’s no surprise that an “alpha” is still buggy and will be for quite a while. Memory leaks are the big issue plaguing the release right now, but it will be ironed out in the next release. The author applauds the fact that 3.0 doesn’t utilize the CPU as much as 2.0 does, but whether or not that’s due to the lack of extensions is unknown.
Source: Wired