In the spirit of a similar page on MDC, this page details the various "branches" and when they were made. In the case of hg, the date is when the new repository was created.
|mozilla-central||Trunk development on Firefox 41 and Gecko 2.0.|
|mozilla-beta||Branch development on Firefox 39 and Gecko 2.0.|
|mozilla-aurora||Branch development on Firefox 40 and Gecko 2.0.|
|mozilla-esr38||Branch development on Firefox ESR 38 and Gecko 2.0.||How To: Releases/Set_Up_ESR_Branch|
|mozilla-1.9.2||Branch development on Firefox 3.6 and Gecko 1.9.2.||branch date: 2009-08-13|
|mozilla-1.9.1||Branch development on Firefox 3.5 and Gecko 1.9.1.||branch date: 2008-12-01|
|HEAD (on CVS)||Branch development on Firefox 3.0 and Gecko 1.9.0.||branch date: 2008-06-01 (kinda; didn't really "branch", development moved to hg)|