If you've noticed YouTube tabs slowing down and becoming quite laggy after an extended time, we believe we've tracked down the cause of this issue and released a patch for it yesterday (134.0.1). Details of the issue and the fix can be found in Bug 1939295.
Shout out to the users who alerted us to this problem, and (as always) everyone here greatly appreciates your support. Thank you.
-Mike Conca
