Unable to start firefox profile manager on MacOS I am trying to start the profile manager for Firefox running the following command in a terminal:

/Applications/Firefox.app/Contents/MacOS/firefox-bin --ProfileManager


But this opens just Firefox. Probably a new session, but I'm not sure. It surely does not start the Profile Manager. Is there anything else I can try to start the Profile Manager?

macOS Mojave, Firefox 72.0.2
To start the Profile Mnager, Firefox must not be running.  Also, the command to start Profile Manager from the command line is:

/Applications/Firefox.app/Contents/MacOS/firefox -ProfileManager


Note, that it's only one dash preceding the option and you don't need to use firefox-bin.  You can also use the short hand version, firefox -P as well.  

Mozilla has excellent documentation on its Command Line Options.