I do have a Facebook account, but I'm not interested in using it here just to save. So, another vote for a cookie.

Off topic, but god I just wish Facebook would disappear. It's ironic that such a popular company with such a huge valuation would produce an immediate and significant benefit to me if it just disappeared overnight.

Also do not have a facebook account and was bummed to see my progress gone.

Why not create one but never post onto it? That's what I did. I don't see any detrimental effects if I create an account but never use it to its full capabilities.

Or, if you want to motivate this particular developer:

"How about you store my progress in a regex! (Which can be put into a browser cookie as an afterthought.)"

Yeah same here. Clicked to a puzzle curious to play with it, saw the notice saying I need to log in to facebook, closed the tab.