Since upgrading to v89 I have found that FF will now refuse to remember its last used window size and location, and FF v88 didn't exhibit the same issue. I will preface this by saying I fully appreciate Windows 10 20h2 is probably partly to blame. I use a ultrawide monitor (3440*1440) and windows10 itself has an utterly crap window size and location issue(since v1809 upto 20H2) with most applications/programs. So to get around that I have been using Windowmanager (http://www.desksoft.com/WindowManager.htm) and/or Ultramon (https://www.realtimesoft.com/ultramon/) to brute force Window pos/size etc. Every application/program that I have created a profile for with the size/location info works perfectly and so did FF v88. But FF v89 is refusing point blank to be told where I want it. Even doing a refresh of FF by nuking the profile folder from (C:\Users\<user name>\AppData\Roaming\Mozilla\Firefox\Profiles) will not resolve the behavior. The only 'sorta' workaround from my side is to run the monitor in dual-screen mode (2x 1720*1440), and at this point FF v89 will only behave itself for the first launch of the browser. If I launch additional FF v89 windows, the same bloody off to the right and up behavior is back. And secondly even setting the shortcut to always launch FF v89 as maximized does not work, FF v89 again refuses to behave and does wtf it wants to do. So if resetting FF completely does not fix the issue, this suggests an issue with FF v89 or a comparability issue between it and Windows 10 20h2