Note that `--no-remote` breaks starting new browser windows from outside, which users normally want.

I'm starting to think that setting the `HOME` environment variable is the only way to really make things isolated - this still won't handle `~insertusernamehere` but basically everything else respects it.

--no-remote doesn't do anything anymore. It was removed about a year ago if memory serves.

I do `open -n "/Applications/Firefox.app" --args -p myprofilename` and that does the trick on mac

On windows powershell I do Start-Process "C:\Program Files\Mozilla Firefox\firefox.exe" -ArgumentList "-P default-release" Which is the exact same idea.

How does that integrate with the "Dock" or menu bar at the bottom? (new to Mac)

Yes, I tried that and everything else. Either it refuses to launch with `--new-instance` or (from memory, in the case of your command) subsequent `--new-tab`s may open in the wrong profile. Presumably due to the order in which the original instances were created. The point is that the system turns on these UIDs, which are not paths or even hashes of paths.