I personally use Firefox's "Multi-Account Containers" which Mozilla advertises as "an improved version of the Containers feature built into Firefox and available to advanced users". It requires an official add-on though: https://addons.mozilla.org/en-US/firefox/addon/multi-account....
ffhhj|4 years ago
Temporal_Trout|4 years ago
The docs are here:https://support.mozilla.org/en-US/kb/containers#firefox
The only thing that stands out to me is "Containers are disabled in Private Browsing windows and when Never Remember History is selected in your privacy settings."