After each major update there is always some people who are confused by the numbering scheme used for Thunderbird. Common question is why did the version number just jump up by 7? Thunderbird follows the Firefox ESR release numbering which means there is major release every 48 weeks or 7 regular updates of Firefox/Gecko. So, next big update will be Thunderbird 45 in March 2016. This is the tentative schedule for the next year:
- June 30th: Thunderbird 38.1.0 (Gecko 39)
- August 11th: Thunderbird 38.2.0 (Gecko 40)
- September 22nd: Thunderbird 38.3.0 (Gecko 41)
- November 3rd: Thunderbird 38.4.0 (Gecko 42)
- December 15th: Thunderbird 38.5.0 (Gecko 43)
- January 26th: Thunderbird 38.6.0 (Gecko 44)
- March 8th: Thunderbird 45.0.0 (Gecko 45)
- April 19th: Thunderbird 45.1.0 (Gecko 46)
Mozilla switched the numbering back in November 2012 with Thunderbird 17. Then in September 2013 the new branch was Thunderbird 24, July 2014 was Thunderbird 31 and then May 2015 we moved to the now Thunderbird 38 branch. The reasoning for the numbering changes (and to follow the ESR) was because like the ESR builds, there are no new features added (just bug fixed and security patches) with each six-week standard updates of Thunderbird. Instead all the new features are lumped into the new major release once a year.
Version numbers are denoted as X.Y.Z
- X is the major version/branch number. This release happens about once a year and includes new features plus any patches and updates
- Y is a standard update. These are the standard every six weeks patches and updates to the current branch
- Z is an emergency update. Something critical was broken or a major security issues was patched to warrant a special release in between the six-week cycle
Part of the confusion this time around was because there was never an official release of Thunderbird 38.0.0. Instead Thunderbird 31.7.0 contained the patches and updates that would have been part of Thunderbird 38. Thunderbird 38.0.1 which was released last week contained the new features (Integrated Lightning, OAuth2 authentication for GMail, removal of SHA-1 hashing support, etc.). There was a Thunderbird 38.0.0 build, but during the Beta stages it was determined there were too many bugs as a result of the changes made in Gecko 38 that there was no way to push out a stable release on the planned May 12th release date (later pushed out to May 26th).
The next planned and regularly schedule release will be Thunderbird 38.1.0 on June 30th, 2015.
Update 07/08/2015: Thunderbird did away with the Thunderbird ESR branch in June 2014 as it was redundant to have two versions of the same build. Thunderbird continues to follow the Firefox ESR release schedule.