It works for me in Edge, Firefox, and IE, I presume a new chromium release broke something. You could try opening the browser's devtools (ctrl+shift+J or F12 I believe), selecting the iframe element the game is within, and typing:
$0.requestFullscreen();
into the developer console.
Or simply try a different browser/desktop version.
However, could you elaborate on the option refusing to work at all? Does the switch not move at all?
EDIT: there's a command for going full screen in the game dev console (that you bring up with F2):
fl
you could try it as well.