This is something to do with running your site outside of a server. When you just “double-click” the file, it runs as
file:/// instead of
http://. Browsers have harsher rules when calling outside resources this way… which means CORS needs an extra push (if it will work at all). Research
origin:* for possible solutions (one possible solution).
The good news is that as soon as you put it on a proper server again, it should work properly.