You probably had the Video DownloadHelper add-on in your previous version of Firefox. In the new Firefox 8.0 version, add-ons are not automatically enabled. You may already have the add-on installed, but it may be disabled. Check your add-ons page and enable that add-on or just reinstall it. You can do so by going to \Firefox\Add-ons. '''Edit:''' Adding this [https://support.mozilla.com/en-US/kb/Customizing%20Firefox%20with%20add-ons?s=installing+add-ons&r=2&as=s Add-ons Help] article as well.