> AFAIK only Safari has 3rd party cookies disabled by default. Safari's "3rd party cookies disabled" behavior is not the same as the Firefox one. Firefox's bl

> AFAIK only Safari has 3rd party cookies disabled by default. Safari's "3rd party cookies disabled" behavior is not the same as the Firefox one. Firefox's blocks third-party cookies (though it's hard to tell whether it just blocks _setting_ or also blocks _sending). Safari does something where they send the in some cases, but I'm having a hard time determining which cases, possibly because they've changed behavior a few times. At one point they blocked third-party cookies, _unless_ the third-party site has previously been visited as a first-party site. What this meant in practice is that Safari wouldn't block third-party cookies for things like Facebook or Google that you probably have visited as a first party. At this point they _may_ be doing double-keying of cookies instead (top domain and third-party domain as key, not just the third-party domain). As I said, it's a bit hard to tell from the documentation out there, which is conflicting and contradictory, and I have no time right now to go read the source. And even then they might only be doing double-keying in the "never visited as first party" case... The point of all of which is, "blocking third party cookies" is not a well-defined thing and different browsers mean quite different things, with different web compat impact and site breakage, when they say they do it.