Cross-domain cookies do not work in Safari
The user authentication information is stored in cookies; however, Safari does not (by default) allow cross-domain cookies to be set. Without the cookie, the app loses the user authentication information across requests. See http://anantgarg.com/2010/02/18/cross-domain-cookies-in-safari/.

Lorsque Facebook explique aux développeurs comment contourner la fonction Do Not Track de Safari – Facebook est dans le même bateau que Google – Best Practices – Développeurs Facebook