This is redundant now that Firefox has Total Cookie Protection (AKA Dynamic First-Party Isolation) on by default[1].
[1] https://blog.mozilla.org/en/mozilla/firefox-rolls-out-total-...
[1] https://blog.mozilla.org/en/mozilla/firefox-rolls-out-total-...
I've tried switching off different settings with no luck. Does anyone know if anything can be done? I am trying to use Firefox developer edition