From the 'how many Beta's makes a release?' files:

Mozilla is now planning on adding a fourth Beta to its oft delayed Firefox 3.1 open source web browser.

Firefox 3.1 will be the first major update to Firefox 3.0.x which was first released in June of 2008 after five alphas, five betas and three Release Candidates. Firefox 3.1 development released have been stalled at Beta since the Beta 2 release in December of 2008. The plan now according to Mozilla Developer Mike Shaver is to push out a Firefox 3.1 Beta 3 next week with the Beta 4 to follow 6 weeks after that.

Firefox 3.1 is set to include a new JavaScript engine, new HTML 5 features as well as a Private Browsing (aka Porn Mode).

Safari 4 beta 都已經出來了，如果Firefox 3.1（或3.2）還不改進TraceMonkey，Firefox 的使用人數都會轉去Safari 了。