That article and screenshot is about doing a custom install on Windows. It is not common to do a custom install on Mac. Any special reasons for doing this ?

Doing a custom install on Mac OS X is basically dragging the Firefox application out of the DMG file to the desktop and rename the folder. You can drag the renamed Firefox application folder to the Applications folder like you would normally install Firefox. You can possibly eject the DMG file and and trash the installer.

You can use the terminal to create a new profile.

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

Make sure that no profile is selected as Default=1 in profiles.ini to make the Profile Manager show when you start Firefox.

• https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

Our products run under Windows, so this is for a Windows (10P) install.

I sent the email using MacMail.

https://support.mozilla.org/en-US/kb/custom-installation-firefox-on-windows

It sounds like you got the small online stub installer from mozilla.org. You can get the full offline setup for Windows at https://www.mozilla.org/firefox/all/ as just pick the preferred installer and language.