Hmm. When I locks up, I can restart and reload the game, somehow I don't think that is how it is supposed to work, but it is a fix.
Although we're glad that you can continue to play it is definitely not supposed to be happening!
Have you noticed any pattern about when this happens? (scene or music change for example) Would you mind telling us what browser you're using? We can start there try and replicate this.
Thank you for letting us know.