Just to clarify, what do you mean by “hidden”? It’s been having the options -P, -ProfileManager , -profile for decades now.
Yeah, that is a pain in the butt - you wouldn't use that in a normal workflow. Plus you couldn't tell which window was in which profile! you needed a extension to give the windows labels, but they still got mixed in the taskmanager/dock etc.. it wasn't really usable in normal multiprofile concurrent workflows. As proof, your example firefox profile manager is empty!
As a motivational example right now I have 25 profiles, for 25 services I use, and i swap between them all the time.
