Here's my take on Facebook (disclaimer: I work for Google, these opinions are purely my own and not representative of the company, yadda yadda yadda). Display advertising works best when you have sufficient, quality inventory (publishers whose sites serve ads) such that you attract advertisers in sufficient quantity and quality. Targeting in display ads works because from the publishers, the intermediary has informat…
"Visit any Like-enabled site and you see a small piece of content from Facebook that tells Facebook all the sites you visit. It's a tracking cookie like any other and personally I have no problem with that" I understand that you work for Google and that not holding this opinion would mean that you have to conclude that your employer is also very much in the wrong. But how do you justify it? It's clearly not informati…
Safari blocks _setting_ third-party cookies by default. It does not block _sending_ of third-party cookies, last I checked.
Firefox's third party cookie setting blocks setting and sending and doing that _definitely_ breaks some sites (e.g. some e-payment systems). Hence it not being enabled by default.
The problem is that the Safari approach is not good enough to prevent the tracking issue where Facebook is concerned: As long as you visited Facebook directly so that it got a chance to set a cookie, that cookie will get sent every time the Like button is fetched. So at that point Facebook knows who you are (via the cookie) and which site you visited (because the Like button itself has access to that information).
The Safari approach _does_ help deal with tracking via ad networks that you don't have any kind of first-party relationship with, since those would never get a chance to set a cookie to start with. So it's definitely a good idea, and I wish more browsers would adopt it. But it doesn't help with the Googles and Facebooks. Unless, of course, there were some sort of requirement that the "user-facing parts" and "ad parts" of those organizations use different domains. Would be pretty hard to get something like that written down properly, even.