Firefox 3.0 has had the first Release candidate made available on their website. If you are currently running a beta of Fox3 - this might be handy to know.
Note the software is still being tested and regardless how stable people tell you a piece of software is - using a Beta or a RC build on a production or live system - you accept that there are most likely still problems with the program. (ie. If you are going to test - make a backup, and don't do it on a live/production/business system).
(for those interested http://lifehacker.com/376551/the-complete-field-guide-to-testing-firefox-3 )