Thunderbird Release Numbering Change

Due to the changes in the development plans for Thunderbird announced last year, Mozilla has changed the numbering scheme of future Thunderbird releases. Most of us were expecting to see Thunderbird 18 (built off of Gecko 18) released on January 8th, but instead were updated to 17.0.2 version. Future Thunderbird releases for the most part are going to be maintenance updates and not actually being built off a new version of Gecko has been the case since the introduction of RapidRelease back in May 2011.

The numbering is now going to follow that of The Thunderbird ESR (extended support release) aka Thunderbird for Organizations which follows the Firefox ESR numbering. Back in November Thunderbird ESR builds were introduced for Gecko 17 and version 17.0.1 was released. There was one final ‘overlap’ Gecko 10 build (version 10.0.12esr) back in November at the same time Thunderbird 17.0.0esr was released.

The releases will still be every six-weeks and will continue with the 17.0.x numbering scheme. In September there will be two releases; a final release on the 17.0.x branch and the first release on the 24.0.x branch. Below is the tentative release schedule. Note that numbering could change as the result of an unplanned emergency release of Firefox and/or Thunderbird. This was the case with 17.0.1 which was released for Firefox only.