Start Firefox from Terminal on Mac OS X (Snow Leopard)

These examples will open Firefox, open a specific website, or browse your user's home directory.

open -a firefox
open -a firefox -g http://news.google.com
open -a firefox -g $HOME

The problem with your second attempt is that your path does not include the .app extenstion.

Try using either

open -a /Applications/Firefox.app

open /Applications/Firefox.app

You want to run /Applications/Firefox.app/Contents/MacOS/firefox-bin

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