Believe it or not but this old script still works perfect. It's even better than many other as it stop the video immediately. It also works in play list.
Remember too deactivate it before you watch a playlist if you want the videos too autoplay.

Me encanta este script, aun que ya esta algo viejito sigue funcionando perfectamente.

amigo me gustaria que lo actualises y lo agas compatible para opera

gracias

Este es el script que mejor funciona en el nuevo Youtube aunque falla algunas veces en calidad 480p...

thank you!

Works just as advertised.