Okay! I'll try it again to see if it's always like that or if I can trigger it again.
I think I discovered the issue. I still need to do more tests but it seems like the quit button stops working after you either go to comics, movies, or the extra section. My theory is that because those ones use the internet, the "close window" function that the Quit button uses is trying to close THOSE windows instead of the game itself. It's difficult to explain but it might take some more time to fix. For now, if the quit button doesn't work, in the reuploaded version of the game, it will automatically turn off full screen if you're in full screen allowing you to press the X button at the top.