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We have a lot of internal jargon, acronyms and internal project names at Mozilla. This glossary lists some of the key terms we use in the Release Management team.

Approval Flag

A flag that represents a security approval or uplift request on a patch.


Short for Chemical Spill. A chemspill is a rapid security-driven dot release of our product.

Channel Meeting

A twice weekly time to check in on the status of the active releases with the release team.

Dot release

A minor release in which only the version number behind the dot is changed, hence its name. For example, in Major Release 101 the first Dot Release is 100.0.1

Dot releases are usually done to fix a stability (top-crash) or a security (Chemspill) issue and are done outside of the usual release dates and release train cycle.

Early Beta

Beta releases with the features gated by EARLY_BETA_OR_EARLIER enabled. The first 2 weeks of Beta releases during the cycle are early beta releases.

Firefox ESR

The official release of Firefox for enterprise. ESR is built off mozilla-esr and is released twice a year. Updates for security and stability fixes are released every 4 weeks.

Firefox Beta

Early stable releases of the next version of Firefox. Released to a wider audience before it becomes the official release. Beta is built off mozilla-beta and is released three times a week. Each upcoming release spends 4 weeks on Beta before moving to Firefox Release.

Firefox DevEditon

A version of Firefox Beta that includes developer tools.

Firefox Nightly

Releases that contain experimental features and are built off mozilla-central. Nightly builds are automatically built and released twice daily to the Nightly Channel. Each upcoming release spends four weeks on nightly before moving to Firefox Beta.

Firefox Release

The official release of Firefox to general availability. Release is built of mozilla-release and is released every four weeks.


Internal project name used to represent the Firefox Android Application


Acronym for Go to build. Mostly used in the release schedule communication ("Go to build on March 18"), this means that we initiate the building of a specific release.

Merge Day

This is the day in the release cycle when we merge mozilla-central into mozilla-beta and mozilla-beta into mozilla-release. That both means the release of a new version of Firefox and the beginning of a new development cycle on mozilla-central (the version numbers on mozilla-central and mozilla-release are bumped up). During the cycle, there is a first merge of mozilla-central into mozilla-beta used to produce Dev Edition Beta 1 and 2, this is called the "first merge". During the first merge, the version number on mozilla-central is not bumped.

Nightly soft code freeze

Last week of the nightly cycle on mozilla-central just before the merge to beta during which landing risky or experimental code in the repository is discouraged.


Name of the internal application used by release managers to prepare and publish release notes. The data in this application is fetched by


Acronym for Release-drivers.


Acronym for Release Candidate. A build from the release branch that is considered a candidate to be pushed to general availability, pending QA approval.

RC Week

The week prior to release go-live is known as RC week. During this week an RC is produced and tested.


Short for Release Engineering.


Short for Release Management.


Short for Release notes.


Acronym for Regression Engineering Owner


Shipping a release to a percentage of the release population.


Name of the internal application used by release management to store all the metadata relevant to a release (version, code and l10n shas, date, platforms, chemspill or not…) and make it available to release engineering tools for releases. The data is also exposed publicly as JSON files as part of a public API called [[1]].

Status Flags

A flag that represents the status of the bug with respect to a Firefox release.

String Freeze

Period during which the introduction, modification, or deletion of strings exposed to the end-users is not allowed so as to allow our localizers to translate our product.


Internal name of the web application which processes crash data at

Train Model

Our release process Mozilla has a fixed-schedule release model known as a Train Model. We release a new version of Firefox to general availability every four weeks. Each release goes through a cycle of 4 weeks on Nightly, 4 weeks on Beta, and then 4 weeks on Release.

Tracking Flags

A Bugzilla flag that shows whether a bug is being investigated for possible resolution in a Firefox release. Bugs marked tracking-Firefox XX are bugs that must be resolved one way or another before a particular release ship.

Throttle/Unthrottle a rollout

Throttle is restricting a release rollout to 0% of the release population, users can still choose to update but are not updated automatically. Unthrottle is removing the release rollout restriction.


Backporting a patch from a development branch to a more stable branch.


Short for "what's new pages". The page that is displayed in our product when they get a major update. These pages are hosted on for our Desktop products and on Google Play, Apple AppStore and other software stores for mobile.