I'm not znpy so I don't know why they don't like containers.

But I prefer profiles myself, as I have different extensions in different profiles and I get the two completely separate instances of Firefox, while containers are just separate tabs instead.

I don't think containers are awful though, they are just less useful for my use case than profiles.

I sometimes have issues with the profiles too though. If I have both profiles running concurrently and I click a link from a different application, I get an error that "Firefox is already running" and it freezes up the window with my primary profile.

Do you ever experience that?

Strange, haven't had that issue myself, running firefox-75.0-1 on Arch Linux. You probably should report that to Mozilla, if you can.