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  • Releases
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On this page
  • Thunderbird Release Train Model
  • General Release Cadence
  • Release Channels
  • Thunderbird Daily
  • Thunderbird Beta
  • Thunderbird Release
  • Thunderbird ESR (Extended Support Release)
  • Stabilization Milestones
  • Daily Soft Code Freeze
  • Pre-Merge Reviews
  • Sample Release Timeline for Thunderbird 136
  • Thunderbird Milestones Calendar

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  1. Releases

Release Cadence

PreviousThunderbird ChannelsNextUplifting Fixes

Last updated 1 month ago

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Thunderbird Release Train Model

Thunderbird follows a release train model to ensure timely and predictable releases. This approach allows for regular feature rollouts, stability improvements, and bug fixes.

General Release Cadence

The general release cadence consists of 4-week cycles, with each branch corresponding to a specific release channel. Each branch, starting from comm-central, is based on the previous branch.

Release Channels

Thunderbird Daily

  • Release Timeline: A new major version of Thunderbird Daily begins every 4 weeks.

  • Releases: Thunderbird Daily is automatically released on a daily basis from comm-central.

Thunderbird Beta

  • Release Timeline:

    • A new major version of Thunderbird Beta begins every 4 weeks.

    • 4 weeks after Daily starts for a new version, comm-central is merged into comm-beta.

  • Releases: Thunderbird Beta for this version is released weekly for the next 3 weeks.

    • Beta 1: Includes the merged code.

    • Beta 2 and above: Include any new uplifts.

Thunderbird Release

  • Release Timeline:

    • A new major version of Thunderbird Release begins every 4 weeks.

    • 3 weeks after Beta starts for a new version, comm-beta is merged into comm-release.

    • 1 week after this merge, the monthly Thunderbird Release is published.

  • Releases: Thunderbird Release is released every 4 weeks, with point releases as needed every 2 weeks.

Thunderbird ESR (Extended Support Release)

  • Release Timeline: The code from comm-release is merged into comm-esr<version> once a year.

  • Releases: Thunderbird ESR is released every year, typically in July, with point releases as needed every 2 weeks.

Stabilization Milestones

Daily Soft Code Freeze

  • A 1-week soft code freeze occurs for comm-central prior to merging into comm-beta.

  • During this time:

    • Risky code should not land in comm-central.

    • Features controlled by a feature flag that were disabled in Daily should not be enabled.

Pre-Merge Reviews

  • Prior to both merges, reviews are conducted for all changes included in the merge.

  • Code may be backed out if:

    • It is deemed too risky.

    • It introduces new crashes or high-severity bugs.

    • It reduces the overall quality of Thunderbird.

    • It introduces a bug and a follow-up fix cannot be provided in a reasonable timeframe.

Sample Release Timeline for Thunderbird 136

Milestone
Date

Thunderbird 136.0a1 starts

Jan 6

Thunderbird 136.0a1 soft code freeze

Jan 27–Feb 3

Thunderbird 136.0a1 pre-merge review

Jan 30

Thunderbird merge 136.0a1 central → beta

Feb 3

Thunderbird 136.0b1

Feb 5

Thunderbird 136.0b2

Feb 12

Thunderbird 136.0b3

Feb 19

Thunderbird 136.0b4

Feb 24

Thunderbird 136.0b4 pre-merge review

Feb 24

Thunderbird merge 136.0b4 beta → release

Feb 25

Thunderbird 136.0

Mar 4

Thunderbird 136.0.1

Mar 18

Thunderbird Milestones Calendar

You can view Thunderbird release milestones on the .

Thunderbird Release Calendar