Firefox 12 is now available for download. You can update it manually or just visit http://www.mozilla.org/en-US/firefox/new/
Download new Firefox 12 by clicking the image or just visit http://www.mozilla.org/products/download.html?product=firefox-12.0&os=win&lang=en-US for en-US version.
It is always advised to update latest version for security reasons. Even beta, major releases are always worth to try.
Check Firefox 12 release notes from: