If it isn't working, *READ* the help. Uninstall and re-install. Now it works again. YouTube could easily block, don't blame the author of this add-on if it doesn't work for you.

I literally made a Firefox account just to give this extension five stars. THANK YOU DMITRY
EDIT: If it's currently broken for you, it might be because of YouTube's new UI they're rolling out. I downloaded the Enhancer for YouTube add-on and it now works again.

huh... neat... it worked~ bless you developer~

A hero from the shadows

Very very good. Well done!