From the Mozilla Developer Centre:

Whenever we’re asked “when is Firefox going to be released” we endeavour to answer to the best of our abilities, but the truth of the matter is that we’ll only ever ship “when it’s ready”. We have a lot of indicators that help us understand when the product is ready for release: feedback from our pre-release milestones, excitement in the community and the press, availability of compatible Add-Ons, and a large active beta community helping us ensure that the release is compatible with all the various sites on the Internet.

After more than 34 months of active development, and with the contributions of thousands, we’re proud to announce that we’re ready. It is our expectation to ship Firefox 3 this upcoming Tuesday, June 17th. Put on your party hats and get ready to download Firefox 3 - the best web browser, period.

Plus the 3rd Release Candidate is out today.  Unless you’re on a Mac you don’t need it though, as it contains only a single change to fix a Mac-only bug that was causing the system to hang or crash at startup or shutdown.