Mozilla has updated Firefox to version 12, bundling in a special bonus for Windows users: silent updates. Future releases for the browser will no longer require a confirmation from Windows' User Account Control panel (UAC), which could allow the browser to pick up the pace with software updates, since the user won't need to acknowledge them.
The Windows UAC is designed to alert the user when a new application is trying to make changes — Firefox's rapid update schedule can make this annoying (Firefox 11 was released just last month). Firefox 12 installs a service that runs in the background; give it permission once, and it'll serve up browser updates as they become available.
It's a simple tweak, but a useful one: many users might be tempted to click through UAC notifications (or turn the dialog box off altogether) after repeated, annoying announcements. If you'd prefer to retain control over your updates (handy, if you're worried about extensions breaking) you can still opt to be notified with every new update. You can grab the update from Firefox's website.