This is something I've noticed in the last couple of mouths... Initially everything on Firefox runs fine for the first 1-3 hours, but after that the multiple YouTube website video tabs I generally have open, especially the very last YouTube website video tab that's open, or any new YouTube website video tab I open, starts to lag like crazy. Using my mouse to click the play/pause on the video player, or pressing the play/pause function key or spacebar on my keyboard, takes a good 3 or 4 seconds before the input action is registered, and it's not just that but the entire UI of the web page itself is slowed down. Doing simple things like clicking on-screen buttons to navigate, and scrolling down to load comments, or scrolling down to load other video thumbnails etc etc, takes a good few seconds to actually work. In general the YouTube tab(s) become very slow and unresponsive, and it's not just the video player on the tabs - it's the YouTube website in general that is affected. I don't see a substantial difference in CPU or RAM in Task Manager when these 'slow downs' occur, but the fan speeds inside my mini PC do spin louder and louder. For whatever reason this problem ONLY happens with YouTube. Other websites via other tabs tend to run and function just fine 24/7. I'm running the latest 133.0.3 version of Firefox, and my system specs are as follows: Processor: Intel(R) Core(TM) i7-10700T CPU @ 2.00GHz Storage: 595.2 GB Installed RAM: 16 GB (15.7 GB usable) Other people have also reported similar things over on Reddit with regards to Firefox and YouTube.