Mozilla has just released Firefox 12 to the release channel, six weeks after Firefox 11. Version 12's chief addition to the browser is a new auto-updater for Windows users, which no longer requires administrative privileges to install updates - you'll be prompted once by the UAC the first time you install Firefox, and the browser will update silently after that. If you still want to be notified before updating, you can revert to the old behavior by unchecking "Use a background service to install updates" in Firefox's update preferences. The new auto-updater appears to be a Windows-only change, at least for now; the updater's behavior is unchanged in OS X and Linux.

The other major user-facing change is in Firefox's developer tools, which Mozilla claims introduces 85 improvements, including the addition of line numbers to the Page Source window. Other minor changes include a WebGL performance issue under OS X on certain hardware and a smattering of security fixes, a list of which can be found here.

More information on these changes, as well as on other fixed bugs and known issues, is available in the release notes linked below. Firefox 12 is available for Windows XP, Vista, and 7, as well as OS X 10.5 (Intel), 10.6, and 10.7 and most Linux distributions.

Source: Mozilla