There are still major issues. I havenâ€™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 â€” and thatâ€™s with no extensions installed.
However, the main reason for the memory leaks, according to the release notes, is the new and improved garbage collection system which promises a much improved memory footprint once the bugs are ironed out.
Most things do work better once the bugs are ironed out.
Check out the paper linked from this blog post. I haven't read this one before. More later if I get the chance, maybe even some code.