Milestones and key data for Firefox 159

Release Date	October 27, 2026
Release Owner	Ryan VanderMeulen
Corresponding ESR releases	153.6.0 · 115.44.0^?
Nightly cycle length	2 weeks
Beta cycle length	2 weeks
Bugs fixed in nightly	1257
Uplifts in beta	197 (1 backout)
Uplifts in RC	5 (0 backouts)
Uplifts in dot releases	0 (0 backouts)
Total number of uplifts	202
Betas	5
Release Candidates	1
Dot releases	0
Release notes	General · Developer · Enterprise

Key Milestones
Nightly start	September 29
Beta start	October 12
159.0 ^{66% adoption - 100% rollout}	October 27
Planned 159.0.x ^{Desktop and Android} The deadline for uplift requests is EOD on the Friday prior to go-live	November 3

Milestones
159.0 branch is created The `firefox-v159.0` branch is created from the `main` branch. `version.txt` is bumped to 159.1 on `main`. Any further code change for the 159.0 release now requires an uplift request.	October 16
159.0 release candidate is created The 159.0 release candidate is created based on the `firefox-v159.0` branch. This build might contain additional uplifts. Additionaly, the 158.3 release is tagged as shipped.	October 16
Preliminary QA sign off on 159.0 QA gives a preliminary sign off on 159.0. If it is green, we push the build to the External Beta Testers group. Otherwise, the dev team fixes the issues reported by QA, uplift them to the release branch and we build another Release Candidate.	October 19
Final QA sign off on 159.0 Release notes ready QA gives its final sign off on 159.0. If the sign off is red, the dev team fixes the issues reported by QA, uplift them to the release branch and we build another Release Candidate.	October 20
159.0 sent to Apple Store We submit 159.0 for review to the Apple Store. If we don`t have a working build by the end of the day, we may not ship this week.	October 20
159.1 branch is created The `firefox-v159.1` branch is created from the `main` branch. `version.txt` is bumped to 160.0 on `main`. Any further code change for the 159.1 release now requires an uplift request.	October 22
159.1 release candidate is created The 159.1 release candidate is created based on the `firefox-v159.0` branch. This build might contain additional uplifts. Additionaly, the 159.0 release is tagged as shipped.	October 22
159.0 is shipped 159.0 is shipped on the Apple Store at 3:00 AM UTC with a phased 7 days rollout: Monday: 1%, Tuesday: 2%, Wednesday: 5%, Thursday: 10%, Friday: 20%, Saturday: 50%, Sunday: 100%.	October 26
Preliminary QA sign off on 159.1 QA gives a preliminary sign off on 159.1. If it is green, we push the build to the External Beta Testers group. Otherwise, the dev team fixes the issues reported by QA, uplift them to the release branch and we build another Release Candidate.	October 26
Final QA sign off on 159.1 Release notes ready QA gives its final sign off on 159.1. If the sign off is red, the dev team fixes the issues reported by QA, uplift them to the release branch and we build another Release Candidate.	October 27
159.1 sent to Apple Store We submit 159.1 for review to the Apple Store. If we don`t have a working build by the end of the day, we may not ship this week.	October 29
159.1 is shipped 159.1 is shipped on the Apple Store at 3:00 AM UTC with a phased 7 days rollout: Monday: 1%, Tuesday: 2%, Wednesday: 5%, Thursday: 10%, Friday: 20%, Saturday: 50%, Sunday: 100%.	November 2