Pressing a button may interrupt the process.
If the game is unresponsive for over 60 seconds, click to DELETE ALL DATA.
(PS, only try this after several failed attempts.)
Your old data will be displayed below in a readable format. Copy and save it somewhere because you can use it to resume from where you left off.

Click here to load old states:
IF ALL ELSE FAILS: Click on View -> Developer -> Javascript Console
Run the following command if you wish to attempt to retain your save data:
var x = JSON.stringify(states); clearAllData(); localStorage["states"] = JSON.parse(x);

If this doesn't work (it really should), just input clearAllData();