Live hack for those who want to be able to edit save files:
1. open start_game.html with Notepad++
2. Find in the text
if(e==null)return"";var t="";var n,r,i,s,o,u,a;var f=0;e=LZString.compress(e);while(f<e.length*2){if(f%2==0){n=e.charCodeAt(f/2)>>8;r=e.charCodeAt(f/2)&255;if(f/2+1<e.length)i=e.charCodeAt(f/2+1)>>8;else i=NaN}else{n=e.charCodeAt((f-1)/2)&255;if((f+1)/2<e.length){r=e.charCodeAt((f+1)/2)>>8;i=e.charCodeAt((f+1)/2)&255}else r=i=NaN}f+=3;s=n>>2;o=(n&3)<<4|r>>4;u=(r&15)<<2|i>>6;a=i&63;if(isNaN(r)){u=a=64}else if(isNaN(i)){a=64}t=t+LZString._keyStr.charAt(s)+LZString._keyStr.charAt(o)+LZString._keyStr.charAt(u)+LZString._keyStr.charAt(a)}return t
and replace it with
return e
so that the text between the commas looks like this
,compressToBase64:function(e){return e},
3. Now the new saves will be normally readable and editable with Notepad++.
4. For easy viewing of the file, download the JSON viewer plugin for Notepad++, then open the save file and click plugins/JSON viewer/Format JSON
P.S. Don't forget to always backup your files when editing something