You can enable it now in the main release version of Firefox by going to about:config, read and think twice about the warning, search for browser.profiles.enabled and set it to True. It was not without hiccups for me and these profiles are not the sa...
Under the profiles you can choose from on startup (or go to Manage Profiles) there is a checkbox labeled "Choose a profile when Firefox opens." If you uncheck that it will not ask you every time.
The "Profiles" menu option that comes after enabling the new profiles mode seems unnecessary and redundant. It takes up a lot of space on MacBooks with a notch display. There is already a profiles icon in the toolbar that gives the same options and t...