Do a clean (re)install and delete the Firefox program folder (C:\Program Files\Mozilla Firefox\).

Download a fresh Firefox copy and save the file to the desktop.

• Firefox 12: http://www.mozilla.com/en-US/firefox/all.html

Uninstall your current Firefox version if possible.

• Do NOT remove personal data when you uninstall the current version or you lose your bookmarks and other data in the profile folder.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.

Your bookmarks and other profile data are stored elsewhere in the Firefox Profile Folder and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

Yes, you should update to Firefox 12. For whatever reason it seems that your updater just isn't recognizing that Firefox 12 is out (sometimes it gets corrupted). By just downloading it from www.getfirefox.com, and installing it over your current Firefox, you will be updated and be all good to go :)

I had this same issue with Windows Vista Business 32-bit. I went to Help->About and clicked "check for updates", and it told me there were no updates. I clicked it again, and it told me I was up to date. I restarted Firefox and tried it again and it found the 12.0 update. I have also been having DNS issues where my browser keeps saying that it can't find the server name, but when I click "try again", it's ok. I have a suspicion that the updater will simply tell you there are no updates if it fails to contact the server for any reason. It should say "failed to contact server" instead, but it doesn't under some circumstances.