The next release of Firefox, code named Shiretoko and currently in development, will be labeled 3.5 instead of 3.1 as it had been originally planned.

According to today’s Firefox meeting notes, the version bump aims to reflect more accurately the many changes introduced since the release of Firefox 3.0, the latest major release, last summer. These includes several changes to tabbed browsing, significant improvements to web standards compatibility, a deeply enhanced JavaScript engines, and several new privacy related including an all new private mode that allows users to clear all their browsing activities at the end of a session.

The next beta, Beta 3, will still be labeled as 3.1 while all the necessary changes are made on Mozilla’s several development tools.

The code for Beta 3 is now frozen and builds are already being produced. Final release is expected for next week following QA procedures.

It also seems Beta 3 will not be the final beta as it was originally thought, but a fourth beta should follow in the near future with a chance of including some more new besides fixing the about 100 blocker bugs currently identified.

These small new features are a series of very specific developments (sprints) that may be ready on time for Firefox 3.5, including tab searching via the awesome bar, some additional minor Windows theme retouches, an about:me page that profiles a user’s web usage based on his history, the ability to clear history for more precise periods of time, and a few others.

Update: Mike Beltzner, Firefox product lead, clarifies that despite what the meeting notes may have suggested, the version bump is not a final decision at this point.