YouTube Container

 https://addons.mozilla.org/en-US/firefox/addon/youtube-container/

Youtube Container is a fork from facebook container that isolates your Youtube activity from the rest of your web activity in order to prevent Youtube from tracking you outside of the Youtube website via third party cookies.

https://www.ghacks.net/2018/04/11/youtube-container-for-firefox-isolates-youtube-in-the-browser/ 

YouTube Container is a free extension for the Firefox web browser that isolates YouTube domains that you open in the web browser from the rest to improve privacy.

The extension is a fork of Facebook Containers, an official extension for Firefox by Mozilla that isolates Facebook from the rest of the browsing activity to improve user privacy and limit tracking.

Note: Just like Facebook Containers, YouTube Containers requests access to data for all websites even though it appears to be active only on select YouTube domains.