Rated 5 out of 5 stars

I am using Firefox 3.6.8, with the latest Adblock version installed (1.2.1), and it's working fine on Youtube. You may have a corrupted install. Try uninstalling it, then clear your browser cache and download Adblock again.
Great add-on! The one add-on everyone should have installed!

This review is for a previous version of the add-on (1.2.1).  This user has other reviews of this add-on.