Start Firefox from Terminal on Mac OS X (Snow Leopard)
Solution 1:
The problem with your second attempt is that your path does not include the .app extenstion.
Try using either
open -a /Applications/Firefox.app
or
open /Applications/Firefox.app
Solution 2:
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
Solution 3:
You want to run /Applications/Firefox.app/Contents/MacOS/firefox-bin