Thankfully Mozilla works with the Tor Project so that Tor Browser patches to Firefox get uplifted to mainline Firefox, you can read more about those efforts here: https://wiki.mozilla.org/Security/Tor_Uplift And the Tor Uplift tracker: https://torpat.ch/uplift

In this case the relevant preference is privacy.firstparty.isolate = true. Another worth pointing out pref is privacy.resistFingerprinting = true.

In firefox: about:config -> privacy.firstparty.isolate = true

Note that containers provide similar functionality but in a less rigid manner. On the other hand first party isolation has the advantage that it also applies on navigation within a single tab while containers are fixed within a single tab. Currently neither is a superset of the other. If bug 1323873 [0] gets implemented then containers + some scripting by extensions could act as a superset of first party isolation.

[0] https://bugzilla.mozilla.org/show_bug.cgi?id=1323873