Mozilla moves to Google Chrome style slipstreamed releases
In February, Mozilla announced it was planning to increase the regularity of Firefox releases, planning four in 2011. A draft document from Mozilla engineering director Rob Sayre reveals that the organisation's plan to achieve that goal will duplicate the engineering process of Google Chrome's cascade of maturing releases.
At any one time Chrome has a range of "channels", named nightly, developer, beta and stable, which carry different versions of the Chrome browser; each channel being progressively more mature than the preceding one. Features will appear in the nightly, then over weeks, appear in the developer version, then beta and finally stable; by that time, the nightly version will already contain a range of new features.
Sayre's plan for Mozilla is to use a similar structure but named (temporarily) "mozilla-central (or 'nightly'), firefox-experimental, firefox-beta and firefox" and to produce a new version in the "firefox" channel every sixteen weeks. Each channel would have its own Mercurial repository with its own copy of the Firefox source code. Complex new features which take time to develop would be created in the mozilla-central channel but only allowed to move to "firefox-experimental" when they were ready. New features will also need to have a mechanism which allows them to be easily disabled to allow them to be dropped from a later release.
Source: Mozilla Foundation/Sayre To allow the new development process to function effectively, Firefox will have to be able to silently update in the background and avoid interrupting the user. This will have a knock-on effect on extensions which may or may not be compatible with updates; users would not want a silent update to disable an extension. Sayre notes that "this issue will be complicated".
The proposal will also change the handling of security fixes; there will not be maintenance/security branches of each final release. Instead, the security updates will occur as part of the release process alongside features. Firefox 4 will not be pushed into the new development process though. Sayre says Mozilla will be using the existing branch maintenance processes for Firefox 4.0.x updates and fixes.