IIUC this has been well supported by Firefox for a couple years I think, via a first-party extension https://addons.mozilla.org/en-US/firefox/addon/multi-accoun

IIUC this has been well supported by Firefox for a couple years I think, via a first-party extension https://addons.mozilla.org/en-US/firefox/addon/multi-account-containers/ https://addons.mozilla.org/en-US/firefox/addon/multi-account... There's a specific sibling extension for isolating Facebook, too.