Works fine now! Rated 5 out of 5 stars

Version 0.6.7 works fine. Excellent add-on.

This review is for a previous version of the add-on (0.6.5.1-signed). 

Thank you for feedback, but sorry i cant confirm this. This youtube feature working fine for me with latest Firefox and latest addon (0.6.7). Make sure you are using latest versions.