Hrm. It's kind of unplayable on Firefox where the space key scrolls down a page...
Awesome, thanks! In general for web games it's good to preventDefault on the keys you're using: e.g. Firefox has the "search for text when you start typing" option, so any key could scroll the window and take focus away from the game. And of course there are various extensions that use unusual keys for things. So preventDefault is a nice safety net.