That full screen thing is still an issue on Firefox. I also don't see the need for the full screen call at that point - ironically putting the game screen with the error message into full screen manually is the only thing that works :-)
Of course for the time being we can change in about:config 'full-screen-api.allow-trusted-requests-only' to 'false'. Mozilla gives a warning not to change anything in there and I have no clue about the security implications. But it lets you play this game in firefox.
