XnView Software

Ok, thank you. So it's known problem and the developer had some issues to leave that behavior. But it's still possible to emulate alt+f4 when esc.

Hello! I use such setting: General-Startup-Start with file-Open: Viewer-Fullscreen

What really catches the eye is the very sloppy closing of a full-screen photo using the Esc button. There is a flashing of the current photo in different scales and only then closing. If you press not Esc but Alt+F4 ...