Just a general advice for writing HTML games: remember to preventDefault() on all keyboard-related events (keydown, keypress) for all keys you use when your game has focus (add tabindex to your canvas so you'll get focus/blur events).
Otherwise browser's shortcuts could interfere with your game. I have Opera customized with 1-key shortcuts (with no modifier key) and that's a minefield in games that assume keyboard is all for them.
preventDefault() worked in Opera since ancient times. However, Opera took default action on different event than other browsers (keydown instead of keypress if I remember correctly).
Otherwise browser's shortcuts could interfere with your game. I have Opera customized with 1-key shortcuts (with no modifier key) and that's a minefield in games that assume keyboard is all for them.