Update: Mozilla has now officially made the release public, including a blog posting detailing what they have done. Additional features include improved private browsing, performance and stability enhancements and more.
What makes this more interesting is that the group had planned the third beta for release over a week ago, somewhat pushed by pressure from Apple and Microsoft. Unless the build is broken, what's their reason for delaying an official update? It is possible they are simply busy with the concurrent updates for both the 3.1 beta and the existing 3.0.x branch.