I wish Mozilla would add the ability to set User-Agent for the different containers they offer in Firefox with their addon. Would be sweet to set it to Chrome in my YouTube container only.
Not the person you replied to, but I just searched for "User-Agent changer" and then installed the Firefox extension that it found. When I set it to pretend to be Windows/Chrome my Youtube tabs went back to snappy and responsive.
Holy smokes that did the trick. Not that longer loading times were bothering me too much, (It's still less time wasted than ads) but damn it feels nice to load smoothly again.