'C-x 4 4' doesn't work

[butter-radish]

other-window-prefix (C-x 4 4) isn’t programmed to work if the next command spawns a graphical window; this is sensible as most people don’t run EXWM. I was wondering if EXWM could detect when a command run with the other-window-prefix tries opening a graphical window, and spawns it in the other-window?

browse-url-firefox, which comes with Emacs, is one example of a command that always spawns graphical windows but isn’t designed to work with the other-window-prefix.