> And you can't customize the appId so the window manager treats as another firefox window, not a separate app
IIRC that's actually possible on Linux, but a big pain and, like most command line switches, pretty undocumented.
But yeah, Firefox generally sucks for this use case and it's insane. It would be borderline trivial to implement, immensely useful and they've actually gone backwards on this type of stuff in many instances.