Why can't I remove this top entry in the firewall options?
OS X automatically creates firewall entries when a service (like AFP or SSH) is started through System Preferences. 

That's handy, because you don't have to bother with firewall rules. The OS configures the firewall as necessary for the selected services to work. The downside is that those entries can't be edited or removed from within the Firewall pane, you need to stop the service instead, which is somewhat counterintuitive.

Could it be that you have enabled FTP file sharing in System Preferences > Sharing?

If you are using Mac OS X Leopard or Snow Leopard you need to uncheck "Share files and folders using FTP", the firewall entry will then go away (credit: picture from eHow):



(Apple dropped FTP support on OS X Lion, though it can be enabled and disabled through the command line:


To enable and start the service:

sudo launchctl load -w /System/Library/LaunchDaemons/ftp.plist

To disable and stop it:

sudo launchctl unload /System/Library/LaunchDaemons/ftp.plist

To start/stop it when the system is running:

sudo launchctl start com.apple.ftpd
sudo launchctl stop com.apple.ftpd



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