I minimized the Firefox window. When I maximize the same window, nothing happens. A little square flies to the upper left of the screen. I have to open a new window or close the program completely.
I have several tabs in my Firefox window. If I open a new window, the other window stays minimized with just a title in the preview.
Opaite Mbohovái (1)
Try:
Use Restore or Maximize in the right-click context menu of the Taskbar icon to set focus to the Firefox application if you do not see the Firefox window.
Open the system menu of that Firefox window via Alt+Space and see if you can move and resize that window.
If that works then close Firefox (File > Exit/Quit) to save that setting.