> The answer is: you can't. Because containers and profiles are different things.
If that's what you need then just use Firefox profiles then! The thing is, most people don't need that, and containers offert better ergonomics for the majority use-case (like the one described in the post). But if you still need the niche use-case, then go ahead and use a profile in Firefox too.
Then again, they have the problem that they think that it's appropriate to open the last used profile if you start Chrome again, which can lock out inexperienced users out of the other profile since they don't know how to get that one started.
For me the normal solution of creating separate profiles in Firefox is to use Firefox Portable and have each profile live in their own directory / installation.
Additionnaly virtually everybody owns a smartphone which is used for the personnal stuff.
I've got Firefox, Opera and Chrome and each one has different logins :D gotta be honest, didn't even know Chrome and FF can also do that!
Edge's multi-profile support blows them both out of the water though, with the ability to right click tabs and move them between profiles, automatically open links for certain domains in certain profiles, being able to set a default profile for external links, etc...
If more people understood this, we would be asking for better profile support on Firefox and for container support on Chromium, not suggesting containers to people who need profiles or trying to use profiles as if they were tab containers.
I want profiles because they provide exactly what you mentioned: separation. I need different extensions, bookmarks, history, etc. And inside each profile I can use containers if I want to.
