Since Adobe ceased Flash Player's support, I deinstalled it quite some time ago. The problem is that the "Thank you for choosing Adobe Flash Player" page, that should appear only that one time I restart the browser after I deinstalled it, keeps opening every time I open Firefox. It's been weeks now. I have the "Reopen last session" toggled on since I have quite some pages I need to keep open so I can't reset that and start over, so I need another solution.