Rated 4 out of 5 stars

Very good.
But longer videos are not working,
and showing youtube error

This review is for a previous version of the add-on (0.2.1-signed). 

I am aware that some are experiencing some youtube issues, but I am having a hard time fixing that since it's working fine on the computers I tested and develop.

For the longer video issu, this plugin purpose is just to give the video source to firefox, sometimes the video stall when the connection is not fast enough, in that case try selecting a lower quality or save the video with a right click/save as on the "open in a new tab" link.