The second Firefox 3.1 beta release is past due, but already we are hearing that a third beta will be necessary before Mozilla can proceed to a release candidate, as it would give testers more time to try out with recently added features debuting in beta 2 such as Private Browsing Mode, Worker Threads, Speculative Parsing and TraceMonkey.

The open source group also needs more time to work on so-called “blockers” – bugs that are deemed serious enough to hold up code to be frozen prior to a milestone release. The good news is that Mozilla plans to make Firefox 3.1 beta 2 a stable enough release for add-on developers to start testing their code and that all the features arriving in the final release will be a part of this beta.

Mozilla’s Mike Beltzner says that the proposed move could be done without major impact to schedule, with the second beta still expected to be available in early December and beta 3 in early January. Meanwhile, the final version of Firefox 3.1 is set to arrive late in Q1 2009.