Third-party cookies

An ad server embeds itself across many sites and recognizes the same browser on each: the mechanism behind cross-site retargeting, frequency capping, and view-through measurement. Safari and Firefox block third-party cookies by default; Chrome, after years of deprecation plans, walked back and kept them.

#The party is who set it, not what it knows

Third- versus first-party is about which domain wrote the cookie rather than how sensitive the data is; the same platform can operate in both modes, so "we use first-party cookies" is by itself not a privacy claim. For measurement, the quieter half of the story bites harder: the same privacy push shortened first-party cookie lifetimes (Safari caps script-set cookies at seven days), which truncates attribution windows on every stack, consent banner or not.

In practice: Buron's measurement sits on the durable side of this shift, with a first-party pixel and warehouse-side matching rather than cross-site cookies.

What still works after third-party cookies, including the living cookie-lifetime table: Tracking after third-party cookies: what actually still works. The lifetime caps have their own entry: Cookie lifetime / ITP.