How can I disable avahi-daemon?

Upstart startup scripts live in /etc/init, where you can find avahi-daemon.conf. All things listed in initctl list match to scripts in /etc/init, and they are not executable, thus your find missed them.

To disable a Upstart controlled service, see Upstart cookbook on disabling services: either add # to start on line, or use override files (example: sudo sh -c "echo manual > /etc/init/avahi-daemon.override").

sudo systemctl disable avahi-daemon

worked for me on Ubuntu Gnome 15.10

I found that even if I stop avahi-daemon (and avahi-daemon.socket), Firefox always restarts it. However, this works, and disables this annoying daemon permanently:

apt-get remove avahi-daemon