i found this at http://forums.mozillazine.org/viewforum.php?f=38
Go to your profile directory. Under Windows, this will be C:\Documents and Settings\UserName\Application Data\Mozilla\Firefox. Under Macintosh OS X, this will be ~/Library/Application Support/Firefox. Under Linux, this will be ~/.mozilla/firefox/.
Open prefs.js with a text editor, and remove the line containing "update.lastUpdateDate" if it exists. Then start Firefox and turn off all software and extension update preferences (Tools -> Options -> Advanced -> Software Update) - but leave "Allow web sites to install software" alone.
Thanks to Hendikins for this.
Hopefully that should work. If it doesn't, feel free to post your problem in a seperate thread. Thank you!
i hope this helps