To see which profiles are in your user:
ls -lAh ~/Library/Application\ Support/Firefox/Profiles
If you would like to add and / or manage profiles:
/Applications/Firefox\ Developer\ Edition.app/Contents/MacOS/firefox -p
As pr example to launch an instance of FireFox named: Purchasing
do the following:
/Applications/Firefox\ Developer\ Edition.app/Contents/MacOS/firefox -P Purchasing