[londons_explore]

Site B has an iframe back to site A and the 'user 34' cookie can still be read.

All these protections only prevent setting cookies, not reading them again.

[icebraining]

It does prevent them from reading too: "Domains classified as trackers are not able to access or set cookies, local storage, and other site data when loaded in a third-party context." (emphasis mine)

https://blog.mozilla.org/security/2018/10/23/firefox-63-lets...