User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:65.0) Gecko/20100101 Firefox/65.0 Steps to reproduce: Basically play any video on youtube by clicking open in new tab. Actual results: firefox freezes/hangs for a few seconds. While this is happening, i cant click on other tabs or close or minimize firefox. I had task manager running in background to see if my cpu or hdd or ram reaches 100% resulting in freezing but i wasn't the case. everything was normal. I have also recorded a video of it. here is the link - https://youtu.be/gPOzcZWT5SQ i don't t know if you can make it out from the video, but the mouse movement that you see in between the tabs, its me trying to switch tabs but since firefox is frozen, it wouldn't let me do it. i am on the latest version of firefox quantum 65.0.2 my amd rx 470 gpu driver version is 19.2.2 my windows 10 version is 1809 build 17763.316 this started happening like a week ago. I have not made any changes to my add ons. i was using the following addons before the issue started occuring and i am still using these add ons alternate player for twitch.tv hoxx vpn idm module popup blocker ultimate ublock origin i tried googling to find anything related to my problem. there were posts regarding firefox freezing but none pertaining to my specific case so i decided to care a bug report here. Expected results: Firefox should not have frozen. It should have seamlessly played the video. https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems