I have a fresh install of Firefox. (139.0), but I never not had this problem. I open up the application, open fb.com not scroll a bit not do anything I just wait for the page to load. I run top in terminal and plugin-container goes up to high heavens ~100% CPU. My battery gets hot, and drains infinitely faster than when not using Facebook with Firefox. I have a new M3 with 8gb ram. Lightning fast otherwise. Same problem with my older M1. (irrelevant but Chrome is burning up the CPU for the same reason) My best guess is that the end-to-end encryption is using too much power or whatever Facebook is doing to tap my every blink. Which is fine. I don't do anything excessively bad. The question is here if why can't I just give a certain percentage to the process? I accept the performance to drop a little but having a 120 degree laptop on my thighs at all times and having to charge it daily is not healthy and annoying. About the plugins/extensions I use here is the list of them: none. I have no extensions, plugins, themes, nothing. Brand new fresh install. I'm sure it's reproducible with any Facebook account with end-to-end encryption chat.