Because of the major version bump in mozilla-central, all users of mozilla-central nightlies will be bumped to mozilla-1.9.2 nightlies today. If you want to continue to track the Firefox 3.6 / Gecko 1.9.2 builds no action is required. If you want to track the post-1.9.2 version or absolute "trunk" of Firefox/Gecko you will need to download today's mozilla-central nightly build, found in the nightly area of the ftp server.