Yes, F11 works for fullscreen!
Could you add it to the Controls so people less used to it know about it?
Since this game plays in a different window, there is no Fullscreen button directly in the bottom-right of the embedded window, so it’s important to know.
EDIT: I just noticed the very small bottom bar and bottom-right button to toggle fullscreen added by itch.
In fact, F11 was simply sending Firefox to pseudo fullscreen and the bottom bar remained, I had to click on the fullscreen button anyway - Just clicking on fullscreen button does everything at once, so that was the true thing to do.