If you were using Norton toolbar and other features like Norton Identity Safe in firefox and recently upgraded to Firefox 3, you need to wait for Norton to release the update before you can start using Norton toolbar and features.
Norton had initially planned to release the update on June-19 (Firefox 3 was released on June-17), but the deadline was missed and the update is expected next week. You can check the status on the issue in the thread in Norton Forum.
Update Jul-02-2008 - The fix is released. Norton toolbar for Firefox 3 is now available.
