Also, I have tried indexDB for game saves. It turned out that it allows to save ~60MB per saved item(!) in Google Chrome (desktop version), and over 100MB in FF (tried 100MB – works, did not check if it allows more).
Here is the jquery plugin link:
http://nparashuram.com/jquery-indexeddb/demo/index.html
Working example is in my prototype (see link I’ve sent to you). I blindly save every game object serialized to JSON manually (plugin does it very slowly, for some reason).
So, it allows to have as many save slots as needed (very convenient!), as there seems to be no global limit on total size.