gksudo mousepad fails XUBUNTU

I am trying to get firestarter to run when I boot up Xubuntu. I read the instructions at http://www.fs-security.com/docs/faq.php#trayicon as follows:

Giving the user permission to launch Firestarter without the root password
In order for a regular user to be able to launch Firestarter, the user must be given additional privileges. Edit your /etc/sudoers file in your favorite text editor and add the following line at the end:
username ALL= NOPASSWD: /usr/bin/firestarter
Simply replace username with whatever your login is.

I did that with gksudo mousepad the text editor in Xubuntu. Then there were other instructions on getting firestarter to run on boot up .. but they did not seem to apply. Instead, I put it in Settings Manager under Autostarted Aps .... "applications, settings, settings manager, autostarted apps

add
... then in the "command field" paste gksu /usr/sbin/firestarter
Put whatever you like in "name" and "description"
Press OK
Click Close

and it does not work. I would like to UNdo everything I did, .. but now, gksudo mousepad does not open mousepad .. just goes back to the terminal prompt. So, I cannot edit sudoers. Clicking on Firestarter from Applications button does nothing. No icon on main panel. Don't know if firestarter/firewall is running or not (there is a simple command to find out, but I forgot what it is). I do notice on BOOT, firewall - firestarter is getting loaded "OK".

Specifically, I need to know why gksudo mouspad does not open mouspad (privilaged) anymore, like it did the first time I edited sudoers. Want to fix 'that' and undo everything and try again.