Technical Background The third party sets & reads cookies over HTTP (not in JavaScript). So we need two requests to an external domain to test if third-party cookies are enabled: One where the third party sets the cookie(s) The second, with a differing response depending on whether the browser sent the cookie(s) back to the same third party in a second request. We cannot use XMLHTTPRequest (Ajax)
![Check if third-party cookies are enabled](https://cdn-ak-scissors.b.st-hatena.com/image/square/98d6f053a97a87156775f60757c60865d0f2c47d/height=288;version=1;width=512/https%3A%2F%2Fcdn.sstatic.net%2FSites%2Fstackoverflow%2FImg%2Fapple-touch-icon%402.png%3Fv%3D73d79a89bded)