Where this comes from
Scores are written to your browser’s local storage as you play, under keys beginning fpgg:. They persist between visits on this browser and this device, and they never leave it — there is no server to send them to.
The trade-off is the obvious one: clear your browsing data and these go with it, and a second device starts from zero. That is the cost of not asking you to make an account, and we think it is the right way round.