Very nice addon. Thank you.

Please add the button "on/off extension".

ViewTube + Windows Media Player Firefox Plugin + K-Lite Codec Pack. AthlonXP 2000+ Youtube 720p ~ 70% load CPU.

This is favorite extension for Youtube on Linux, Mac and Windows.
For Youtube Classic View i additionally use the following script with Greasemonkey/Tampermonkey
https://greasyfork.org/en/scripts/384687-disable-polymer-youtube-improved

Some configurability would be nice. I only wanted to use it with some specific websites with horrible HTML5 players. (eg: Dailymotion...) But I can't with the addon

Not sure what the "Direct Video Link" is supposed to do, I only get a "The video should be loading [...]" error message.
EDIT:
There's also no fullscreen button