Release Date | September 16, 2025 |
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Release Owner | Dianna Smith |
Nightly cycle length | 4 weeks |
Beta cycle length | 4 weeks |
Corresponding ESR release | 140.3.0 |
Milestones Desktop, Android & iOS |
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Nightly startsThe first day of the cycle is Merge Day. After merging mozilla-central to mozilla-beta, we bump the nightly version number on mozilla-central and a new development cycle starts for Firefox. A new Firefox Nightly is shipped every 12 hours. |
July 21
In 45 weeks |
Deadline to request accessibility engineering reviewAccessibility engineering review has been requested (using the |
July 25
In 45.5 weeks |
Deadline to request manual QAQA has been informed (via a Jira ticket) about features that require manual testing during the nightly and/or beta cycle. |
July 25
In 45.5 weeks |
Build ready for QA in nightlyFeatures with a QA request are ready for testing to assess feature quality and provide a formal test report by the end of Week 3 of the nightly cycle. |
August 1
In 46.5 weeks |
Build ready for QA in betaIf nightly testing was skipped then features should be in a testable state by this date for beta testing. |
August 14
In 48 weeks |
Soft Code Freeze starts Draft beta release notesWe are nearing the end of the nightly cycle. Don't land new untested features. Risky changes should be avoided after 8:00 AM UTC until after the nightly version bump on Merge Day. |
August 14
In 48 weeks |
QA Test Plan approval dueFor features requiring Nightly testing, the QA team appreciates an earlier sign-off from the project teams. If an early sign-off is not available or testing is required only in Beta, the approval milestone will be the final deadline for any feature Test Plan sign-offs. No feedback/sign-off on QAs Feature Test Plan could result in misalignment on testing scope, incomplete test coverage and invalid bugs. |
August 15
In 48.5 weeks |
String Freeze startsIn order to ensure that our localizers have adequate time to translate strings, please make sure that all string changes have landed by end of day. |
August 15
In 48.5 weeks |
QA pre-merge regression testing doneQA assess build readiness for shipping to Beta by running a set of Regression test cases and shares a test report. Nightly Regression coverage is limited compared to Beta Regression testing throughout the Beta cycle. |
August 15
In 48.5 weeks |
Merge dayThis is the day in the release cycle when we merge mozilla-central into mozilla-beta. This is the end of the development cycle for Firefox 143 and the beginning of our Beta stabilization cycle. |
August 18
In 49 weeks |
Beta 1 Go to buildBuilt manually just after the merge. It is rolled out to 25% of our beta population. Some experimental features are still activated to watch their behavior on a wider population. These experimental features will be deactivated mid-cycle. Uplift requests are open. |
August 18
In 49 weeks |
Beta 2 Go to buildFirst automated beta of the cycle. It is rolled out to 50% of our beta population. Build starts at 13:00 UTC. |
August 20
In 49 weeks |
Beta 3 Go to buildBeta rollout bumped to 100% provided stability is good. Build starts at 13:00 UTC. Stabilization work via uplifts. |
August 22
In 49.5 weeks |
SUMO content creationUser affecting changes were identified and provided to the support.mozilla.org team. The support content for this release can now be created and will be translated before RC week. |
August 22
In 49.5 weeks |
Beta 4 Go to buildBuild starts at 13:00 UTC. Stabilization work via uplifts. |
August 25
In 50 weeks |
Beta 5 Go to buildBuild starts at 13:00 UTC. Stabilization work via uplifts. |
August 27
In 50 weeks |
Beta 6 Go to build Last early betaOn a regular 4 weeks beta cycle, Beta 6 is the last beta with experimental features still activated. Build starts at 13:00 UTC. Stabilization work via uplifts. |
August 29
In 50.5 weeks |
Beta 7 Go to buildExperimental features are no longer activated at compile time. Build starts at 13:00 UTC. Stabilization work via uplifts. |
September 1
In 51 weeks |
SUMO content localizationNew content on support.mozilla.org team is finalized, uploaded to the server and provided to our localization teams internationally. |
September 1
In 51 weeks |
Beta 8 Go to buildLast week of the beta cycle. Build starts at 13:00 UTC. Stabilization work via uplifts. |
September 3
In 51 weeks |
Pre-release QA sign-offA week before the final sign-off, QA shares preliminary test reports for each feature riding the train. This pre-release sign-off can be Green, Yellow or Red. |
September 3
In 51 weeks |
Beta 9 Go to build Last beta uplifts (sec-approval request deadline)On a regular 4 weeks beta cycle, this is the last beta and thus the end of beta uplifts, including security bugs for this release ( |
September 5
In 51.5 weeks |
Release Candidate Go to buildWe merge our mozilla-beta repository to mozilla-release and close mozilla-beta until the next merge day. We then build our Release Candidate from mozilla-release. This is the build we intend to ship a week later unless we need to build a second Release Candidate to fix a major quality or business critical issue. |
September 8
In 52 weeks |
Release Candidate Release notes finalizedOur Release Candidate is shipped to all of our beta population. |
September 9
In 52 weeks |
Release day!We ship Firefox 143 at 14:00 UTC (6AM PST) at 25% rollout. |
September 16
In 53 weeks |
Planned dot releaseTwo weeks after the release, we ship a dot release to address identified quality issues if needed. We may have to ship other dot releases before that date. If this is the case and post-release quality issues are already fixed and shipped, the decision on shipping or not the planned dot release is on the release management team. |
September 30
In 55 weeks |