Hi, I'm having a little difficulty understanding what is happening. Firefox is not running. You click the Taskbar icon to launch Firefox, and the initial window is: * only an icon (minimized to the Taskbar) * only a thumbnail when you hover the Taskbar button * a resizable window that doesn't use the full screen Then when you maximize the window, it doesn't use the whole screen. And when you try to close the window using the X button the program does not terminate. Two ideas initially: '''(1) Try starting Firefox's in its Safe Mode''' In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, any userChrome.css/userContent.css files, and some other advanced features to help you assess whether these are causing the problem. ''With all Firefox processes terminated:'' Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.) A small dialog should appear. Click "Start in Safe Mode" (''not'' Refresh). Any improvement? '''(2) Test a new profile''' Assuming the undersized Firefox window actually operates, this is one method to suss out a settings issue. It takes about 3 minutes, plus the time to test. Inside Firefox, type or paste '''about:profiles''' in the address bar and press Enter/Return to load it. Take a quick glance at the page and make a mental note of which Profile has this notation: '''This is the profile in use and it cannot be deleted.''' That is your current default profile. Click the "Create a New Profile" button, then click Next. Assign a name like Oct2020, ignore the option to relocate the profile folder, and click the Finish button. Firefox will switch your default profile to the new one, so click the '''Set as Default Profile''' button for your regular one to avoid an unwanted surprise at your next startup. Scroll down to Oct2020 and click its '''Launch profile in new browser''' button. Firefox should open a new window that looks like a brand new, uncustomized installation. (Your existing Firefox window(s) should not be affected.) Please ignore any tabs enticing you to connect to a Sync account or to activate extensions found on your system so we can get a clean test. ''Do the problem site(s) work any better in the new profile?'' When you are done with the experiment, you can close the extra window without affecting your regular Firefox profile. (Oct2020 will remain available for future testing.)