While trying to get some updated info on the next release of Thunderbird 3.3 (Miramar) I came across a thread in the Thunderbird Builds forum discussing the numbering change. Simply put, the Thunderbird developers want to have the version numbering match that of Firefox/Gecko. It also sounds as if Thunderbird is going to be following in Firefox footsteps with it’s own rapid release cycle. So the following numbering changes will be taking effect soon:

• Thunderbird 3.3 (Miramar) >> Thunderbird 5
• Builds which will be produced from comm-aurora >> Thunderbird 6
• Thunderbird Nightly (3.4a1pre) >> Thunderbird 7

For those who are unfamiliar with the rapid release cycle here is a brief overview. Major releases are now set for every 18-weeks. This system came about as a result of the major delays with the final Firefox 4 release which resulted from delaying the final product release to get all features functioning. The rapid release cycle has four stages or channels Nightly, Aurora, Beta and Release. Each stage with the exception of Release lasts for six weeks.

• Nightly (comm-central) – These are the ‘freshest’ builds and therefore the most unstable. New features, improvements and bug fixes will be introduced during this cycle.
• Aurora (comm-aurora) – No new features, improvements and bug fixes can be introduced for this version of Thunderbird. Work now focuses on getting these features, improvements and bug fixes stable and working. If it is not working by the end of this six-week cycle it will be moved to the Aurora for the next version of Thunderbird. Typically these builds are somewhat more stable, but can still behave unpredictably.
• Beta (comm-beta) – These builds are release candidates. A six week ‘buffer’ period to address any issues that may have come up during testing of the Aurora builds.
• Release (comm-release) – The final release of the next version of Thunderbird.

It is important to understand that under this new cycle the dates for each cycle will not change. There is no more waiting for features/fixes to land before moving on with the release. If it is not ready by the end of the Aurora cycle it will not be included for that Thunderbird release.

I am hoping this new rapid release cycle will get Thunderbird development moving again. Thunderbird 3.1 was released in June 2010. If Thunderbird follows the exact release cycle of Firefox, then Miramar (Thunderbird 3.3/Thunderbird 5) would be released on June 21st. However, given that Thunderbird has just moved to this new release cycle, Thunderbird releases may not sync with Firefox until Thunderbird 6. Miramar Beta 1 should be released sometime this week. Stay tuned for more release information.