It's annoying these get grouped in the taskbar unlike Chrome profiles. Surely the main use case is to have a "Firefox" and a "Firefox (Work)" pinned separately to the taskbar and have them act as two completely different environments?
Curious, I've been running 2 profiles at once for a while on MacOS and they have separate icons / app management. It's a Windows thing.
A way you might get around this (if acceptable) is to run one profile from a beta or developer version of Firefox which has a separate app path & icon and may result in the behaviour you want.