This article describes what to do if you get a tab named "Firefox Updated" or see the message "You've been updated to the latest version of Firefox." every time you start Firefox even if you haven't updated Firefox.
There are two possible causes for this. You may have that tab saved accidentally as your home page (which Firefox opens each time you start) or Firefox may be having trouble saving to your settings file which results in it not realizing you have already seen the "You've been updated" message.
http://www.mozilla.com/en-US/firefox/4.0/whatsnew/then you have accidentally added the "Firefox Updated" page to the sites that Firefox loads on startup.
Firefox changes a setting in its preferences file to determine whether you've seen the "Firefox Updated" tab. If you are having problems with that file then Firefox will be unable to save this information and will show you the "Firefox Updated" tab each time you start it.