Ok, this has been happening for over a year now. I have tried resetting Firefox, reinstalling it, running it 100% clean without any add-ons and whatsoever. None of these fixed my issue. Whenever I find myself using Firefox for more than a day or so, without closing it, the problems start to occur. First hours of the problem occurring, it starts to freeze from time to time for 1-2 secs, after that it freezes 1-2 times for 10+ secs and finally it just hangs until I force close it. I think it is caused by videos mostly, because whenever the crash happens, I'm browsing a website with a video. Around 80% of the final unending hang happens whenever I play a video. Whenever I go to force-close the browser, I always find it at 30+ CPU usage. Since I am unable to create a Firefox log or some sort of detailed information, I am uploading an image and list (https://pastebin.com/KpVAYjhD) of firefox handles (because GetHandleVerifier function seemed most suspicious and could be related) that I think might help you with debugging the issue.