What is a third-party cookie?

A cookie is a small file a website saves in your browser. A first-party cookie comes from the site you are visiting, and it does useful things like keeping you logged in or remembering your cart. A third-party cookie comes from a different company whose code is embedded on that site, often an ad network. Because the same ad network appears on thousands of sites, its cookie can recognize you across all of them.

That cross-site view is what powered retargeting (showing you ads for a product you looked at) and a lot of conversion tracking. It is also what privacy regulators and browser makers have spent years limiting.

What did Google finally decide about Chrome?

Google had long planned to phase out third-party cookies in Chrome. In July 2024 it changed course, writing: "Instead of deprecating third-party cookies, we would introduce a new experience in Chrome." Then, on April 22, 2025, it announced that it would maintain its current approach to offering users third-party cookie choice in Chrome and would not roll out a new standalone prompt. Users can still block them in Chrome's Privacy and Security settings, and Incognito mode blocks them by default.

Six months later, on October 17, 2025, Google retired most of the Privacy Sandbox, the set of tools meant to replace cookies. Citing low adoption, it dropped the Attribution Reporting API, Protected Audience, Topics, Related Website Sets and others. It kept CHIPS and FedCM, which it said had seen broad adoption, plus Private State Tokens, and said it would keep working on a shared attribution standard through the web standards process.

Share of worldwide browsing by browser, September 2026
  • Chrome66.36%
  • Safari18.27%
  • Edge6.04%
  • Firefox2.8%
  • Samsung Internet2.31%
  • Opera1.77%

Each bar is a browser's share of page views worldwide across all devices; Safari and Firefox block or isolate third-party cookies by default.

Source: StatCounter Global Stats

Other browsers already block them

Chrome's decision does not mean cookies work everywhere. Apple's WebKit team announced on March 24, 2020 that "cookies for cross-site resources are now blocked by default across the board" in Safari. Mozilla made Total Cookie Protection a default for all Firefox desktop users in June 2022. It gives each website its own separate cookie jar, so a tracker can't follow you between sites.

How much browsing does that cover? In September 2026, StatCounter put Chrome at 66.36% of worldwide browsing, Safari at 18.27% and Firefox at 2.8%. StatCounter measures page views, not people, but the point holds: a meaningful share of your visitors, and a larger share among iPhone-heavy audiences, arrive in browsers where third-party cookies don't work.

What this means for your measurement

Cookie-based tracking is now patchy rather than dead. It works for many Chrome users, fails in Safari and Firefox, and is limited by consent rules in places like Europe, covered in Consent Mode and GDPR for advertisers. Inside iPhone apps, Apple's App Tracking Transparency removes another layer.

The practical result is that every ad platform sees a different, incomplete slice of the customer journey, then fills the gaps with modeling. That is one reason platform totals rarely match your actual sales, and why the gap can move when browser shares or settings change. For a small business, the biggest risk is quiet: a report that looks stable even though it rests on a shrinking, shifting sample. If most of your customers use iPhones, assume your platform reports see less of them than of your Android and desktop shoppers.

What to do now

Treat third-party cookies as a bonus you can't count on, and build on things you control:

  • Make payments and orders your scorecard. Our first-party data guide explains why.
  • Tag every link you control with consistent UTM parameters, which rely on the link itself, not on a cross-site cookie.
  • Use the conversion-sharing tools ad platforms offer, which send results from your website or server with customer details hashed (scrambled) first.
  • Check platform-reported conversions against verified revenue every week. Matrix ROI, a product of Smith App Studio, shows those two side by side, day by day, in one currency.