[paranoidrobot]

Have you looked into Firefox Multi-Account Containers[1]?

It met all my needs for multiple profiles. I use it to have multiple concurrent sessions for different sites (eg: one AWS account/role per container).

[1] https://addons.mozilla.org/en-US/firefox/addon/multi-account...

[normalaccess]

This ^

Where I work we are required to have 2-3 Microsoft accounts for security separation. Account containers makes it possible to interact with virtually unlimited profiles all in the same browser window. No need for in-private browsing or multiple widows of chrome or edge, it just works. When you have it configured just right it's a thing of beauty.

[Yodel0914]

Container tabs are the main think that keep me on FF (well LibreWolf) rather than switching to Brave. I find them indispensable.