Progress saves in the browser. You can save from the pause menu. If you do that, and the information is gone the next time you play, the issue is from your browser probably automatically clearing data.
My browser is doesn't do that I checked, when I close the game on the broswer and open it again it restarts me, I might not be the only one, just a suggestion like a backup you could make it so it gives you a code that you can put back to get to your original progress
