Previously: Site A has a facebook Like button, which iframes in facebook.com and sets a third-party cookie for facebook.com. Site B does the same. Site B can see that you previously visited Site A, and if you have a Facebook account, then Facebook can connect your browsing activity on both A and B to that account.
New feature: Site A's Facebook Like button iframes in Facebook, and sets a cookie on facebook.com. This is a different cookie than the one Site B sets for facebook.com. The cookies cannot tell that you're the same person. If you have a Facebook account, your browsing activity on A and B is not connected to your Facebook account.
>Total Cookie Protection offers additional privacy protections beyond those provided by our existing anti-tracking features. Enhanced Tracking Protection (ETP), which we launched in 2018, works by blocking trackers based on a maintained list. If a party is on that list, they lose the ability to use third-party cookies. ETP was a huge privacy win for Firefox users, but we’ve known this approach has some shortcomings. If a tracker for some reason isn’t on that list, they can still track users and violate their privacy. And if an attacker wants to thwart ETP, they can set up a new tracking domain that isn’t on the list. Total Cookie Protection avoids these problems by restricting the functionality for all cookies, not just for those on a defined list.
You can more confidently allow third-party cookies, which means that certain features that broke with the blocking of all third-party cookies will now be able to work, but you maintain most of the protections that you gained when you used to block them.
It's currently controlled by setting `network.cookie.cookieBehavior` to `5`. (There is also a similar setting for private browsing mode which is already 5 by default).
That setting breaks a few things, but mostly works OK. I'm confused which protection level this new capability corellates to.