This is a staging environment for whattrainisitnow.com

«  Firefox 155  »

23% adoption rate
Release DateSeptember 1, 2026
Release OwnerRyan VanderMeulen
Corresponding ESR releases 153.2.0 · 140.15.0 · 115.40.0?
Nightly cycle length4 weeks
Beta cycle length2 weeks
Bugs fixed in nightly 2377
Uplifts in beta174 (0 backouts)
Uplifts in RC0 (0 backouts)
Uplifts in dot releases0 (0 backouts)
Total number of uplifts174
Betas5
Release Candidates1
Dot releases0
Release notes General · Developer · Enterprise
Key Milestones
Nightly start July 21
Beta start August 17
155.0 23% adoption - 0% rollout September 1
Planned 155.0.x Desktop and Android
The deadline for uplift requests is EOD on the Friday prior to go-live 		September 8
Milestones
155.0 branch is created

The firefox-v155.0 branch is created from the main branch. version.txt is bumped to 155.1 on main. Any further code change for the 155.0 release now requires an uplift request.

 August 21
155.0 release candidate is created

The 155.0 release candidate is created based on the firefox-v155.0 branch. This build might contain additional uplifts. Additionaly, the 154.3 release is tagged as shipped.

 August 21
Preliminary QA sign off on 155.0

QA gives a preliminary sign off on 155.0. 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.

 August 24
Final QA sign off on 155.0 Release notes ready

QA gives its final sign off on 155.0. 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.

 August 25
155.0 sent to Apple Store

We submit 155.0 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.

 August 25
155.1 branch is created

The firefox-v155.1 branch is created from the main branch. version.txt is bumped to 156.0 on main. Any further code change for the 155.1 release now requires an uplift request.

 August 27
155.1 release candidate is created

The 155.1 release candidate is created based on the firefox-v155.0 branch. This build might contain additional uplifts. Additionaly, the 155.0 release is tagged as shipped.

 August 27
155.0 is shipped

155.0 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%.

 August 31
Preliminary QA sign off on 155.1

QA gives a preliminary sign off on 155.1. 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.

 August 31
Final QA sign off on 155.1 Release notes ready

QA gives its final sign off on 155.1. 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.

 September 1
155.1 sent to Apple Store

We submit 155.1 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.

 September 3
155.1 is shipped

155.1 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%.

 September 7