Thanks for the feedback. There was more I wanted to do with the game but I ran out of time.
I think you found a bug, because I am able reproduce the same outcome in Firefox and Chrome by taking a character too far off the bottom of the screen. I wrote code for detecting borders but the bottom border never worked, however previously it wouldn't stop game continuance but I see now that it does. Next time I release a more polished version I'll fix the issue.