Third-party (AKA cross-site) cookies are harmful to the web, and must be removed from the web platform. This finding explains why they must be removed, and examines the challenges in removing them. We highlight some use cases that depend on third-party cookies and offer some examples of designed-for...
Comes a little bit late, doesn't it? Why would Google do this? Why would most websites in the world relying on this technology to identify you and sell more ad data do this? Only if a company is privacy focused, such as Mozilla, would do this. Otherwise there is no incentive.
Mozilla has already shipped strict privacy mode by default in recent versions of Firefox so they're already a leg up on this.
Google is currently trying to transition people to its own proprietary method of tracking (where the browser itself tracks you) so they would love it if third party cookies were no longer usable for that.
Mozilla has also added a direct tracking feature (anonimized) to Firefox btw. Not sure what their agenda is.
Websites are irrelevant, if third party cookies stop working in major browsers there's no point in setting them anymore, they'll be ignored.