Probably some form of A/B testing. I used to say the same thing, but specific channels and specific live-streams will now die every 30 seconds using FF+uBlock. I found they appear to do testing on channels they do not like such as those that complain about YT's policy and other channels for reasons I shall not speak of here.

I also use ublock + vpn. Do a quick Google search for "reddit + firefox + youtube not working", you'll see that strings are getting posted much more frequently over the past six months.

Videos play for 10 seconds then stop loading, forced reduced quality, and just generally buggy in several different ways. Many Reddit strings with tons of other people having similar issues.

- https://www.reddit.com/r/firefox/comments/1dgodfn/youtube_on... - https://www.reddit.com/r/firefox/comments/1cjbsmj/youtube_on... - https://www.reddit.com/r/firefox/comments/1bsc0i4/youtube_no...