You can't run two profiles concurrently can you?

I have a container for finances, a container for shopping, a container for untrusted, etc... I can't imagine restarting Firefox every time I wanted to transition between those.

Sure you can. Firefox will treat each open profile as it's own "app/window instance" in a way, so if I want to use my "A" profile, it's running everything under that in it's own window and my "B" profile in another window, etc.

As mentioned, each profile launches in its own window.

I use different themes for each so they are visually distinct.

And different home pages, etc.

I could use different shortcuts for different identities, but I don’t any more. Instead about:profiles is one of my home page tabs for each profile.

That sounds like a lot of configuration to carry around.

Bits don't weigh very much and fit in a convenient laptop shaped carrying case.

It also has the advantage of working the way I expect when I want to do the things I use it to do.

Do containers do that?

That's a tough question to answer because you haven't clearly stated your requirements. It makes it very easy for you to prove that something doesn't work while making it very difficult for someone else to prove it does.

What I meant about configuration is that the onus is on you to manage all of that. I know some people love that level of control but most people it's a burden. Containers are part of your profile and move with you if you're using Firefox Sync. You don't have to copy or maintain multiple profiles or Sync accounts.