Firefox is willing to add specific technical countermeasures to specific domains that are attempting to bypass the tracking policy: "If a party attempts to circumvent the technical solutions we’ve outlined in this policy, we may without notice add additional restrictions to that party to prevent the circumvention." It seems they use the list of tracking domains at https://github.com/disconnectme/disconnect-tracking-protecti... .

(Safari, as far as I can tell, tries to avoid having site-specific policies, so maybe the question is "What is Repixel doing that is exploiting a security bug in Safari, and how can Safari fix it?")