Hi. According to my observations, only Mozilla Firefox and Adobe Reader have this problem so far. Windows 11 + Multi-Monitoring Windows 10 have this Bug not ! Open Firefox, drag the window to the second or third monitor, and suddenly there is another hidden Firefox window on the taskbar of that display. If you move Firefox back to the main monitor, it disappears again. Or you can close Firefox and restart it on the desired monitor. This is an annoying little bug, and I don't understand why Microsoft or Mozilla haven't fixed it yet. It's easy to reproduce and has obviously been around for a while. Since it only affects the two programs mentioned above so far, an MS update will probably not fix it; instead, the developers at Mozilla and Adobe need to address it. Here the Same Topic in Adobe Forum. No bug fix to date https://community.adobe.com/t5/acrobat-discussions/taskbar-phantom-window-when-using-multiple-monitors/td-p/14390169 I hope you release a bug fix soon... but since that hasn't happened yet, I'm afraid it will take a while... I'm surprised, because I'm sure many people are experiencing this annoying problem, and in my opinion it's not a big challenge for your developers. @Mozilla Please Fix this Bug. I know Windows 11 is not better than Windows 10 but Supports End and many Users and Customers used in Future this OS and if you don't want to lose any more market share, it's important to fix this minor bug for ordinary users too. Thanks ;-)