Youtube intentionally degrades the user experience if you use Firefox, at least if you are using a proper ad blocker. And there really isn't much reason to use Firefox if you aren't also using uBlock. So by targeting the users of uBlock+Firefox, YouTube is aggressively degrading the experience of Firefox users. Things I've noticed include:

  1. Every video defaults to the absolute lowest resolution (240 or 320) until I manually switch it to a higher setting.
  2. Occasional (but fairly frequent) 30-second delay before a page loads (loads enough to show a black page, then just freezes for a while.  During this delay, refreshing the page gives the same result.
  3. Rarely, interstitial notice pages threatening vague consequences if I continue to use an ad blocker.