How can I start firefox with a different profile on a Mac?

I have a MacBook Air (Mojave, 10.14.6) and for Testing reasons I need to be able to have several instances of firefox running with different profiles each. At the same time.

How can I achieve this?

Solution 1:

If you mean launching a new instance via Terminal, you can use this:

/Applications/Firefox.app/Contents/MacOS/firefox -no-remote -P "NAME_OF_YOUR_PROFILE"

If you just use the -p option it should open the Profile Manager which should let you select a profile via the GUI, but was always buggy for me (broken blank tabs).

More documentation on the firefox command line options can be found here.