Users who installed a build of Minefield before 24 November and have been using automatic update since then may be in for a surprise: you are no longer using Minefield or testing mozilla-central!
On 24 November, the Firefox code branched: mozilla-central continues as the repository for all new code. After code has been tested in mozilla-central, it is ported to the 1.9.1 repository, a more stable codebase leading to Firefox 3.1.
Right now, we have many more nightly testers on the stable branch (1.9.1) than we do on mozilla-central. But we really want to catch regressions in mozilla-central before they land on the stable branch. If you are a nightly tester, please go download and install a new Minefield build today! (Windows, Mac, Linux).
Update: to figure out whether you’re running mozilla-central or a 1.9.1 branch nightly, just look at the application title: it will say Minefield for mozilla-central, or Shiretoko for 1.9.1. You can also check the About dialog.