YAY! no more memory leaks! I've been running the beta's and release candidates for a few months now and I've been very impressed. It's far snappier to load and open tabs, and much quicker at rendering pages.
Check out the Mozilla blog for more info: http://blog.mozilla.com/ and sign up for download day so we can all help to set a world record :) http://www.spreadfirefox.com/en-US/worldrecord/
Let the countdown begin.