I heard that in Firefox 55 a new feature was introduced as a part of the Tor-Uplift project which added a feature to Firefox called "First-Party Isolation" (FPI) which in Tor is known as "Cross-Origin Identifier Unlinkability".
As described here this feature does the following:
FPI works by separating cookies on a per-domain basis. This is important because most online advertisers drop a cookie on the user's computer for each site the user visits and the advertisers loads an ad.
With FPI enabled, the ad tracker won't be able to see all the cookies it dropped on that user's PC, but only the cookie created for the domain the user is currently viewing.
This will force the ad tracker to create a new user profile for each site the user visits and the advertiser won't be able to aggregate these cookies and the user's browsing history into one big fat profile.
I understand that this feature is still present in Firefox 57 (the current latest version at the time of writing). So how do I get this feature given that it is not enabled by default and not even listed in the official release notes (a serious amount of digging had to be done to even find it)?