The game doesn't advance when I complete the first level. I get "Uncaught (in promise) DOMException: The operation is insecure" in the console. Something goes wrong in `saveProgress`, throws an exception, and then `completeAndAdvance` never gets to call `advancePuzzle()`.
Thanks for the details! This should be fixed now.
I just pushed a fix to catch problems saving progress to localStorage and proceed anyway. Now, affected browser will skip saving progress, but still be able to play.
What browser are you in? I know Safari is often touchy about doing stuff from within an iframe.