Chatzilla is an IRC client available as a plugin for the Firefox browser and works on all platforms for which Firefox is available, including Windows, OS X, and Linux. It can be downloaded for free from the Mozilla’s Firefox add-ons website here.
Open Chatzilla. There are a few ways to go around to this. If you are having trouble, simply open Firefox, click on the "Tools" button (in later versions of Firefox "Tools" may be hidden by default. If such is the case, press on the F10 key to make it appear) and then click on the "ChatZilla" button.
Once you have Chatzilla opened, enter "/server adisc.org 6667 password" in the text box, where "password" is your ADISC password.
If the username Chatzilla attempts to connect to ADISC with is not your ADISC username, you will get an error message telling you that your nickname needs to match your ADISC username. If this happens, use the command "/nick username" where "username" is your ADISC username. Chatzilla should automatically attempt to reconnect within a few seconds.
Once you connect, your screen should look something like this:
Now, click on the "ChatZilla" button at the very top left of the screen, and then on "Preferences...".
Now, click on "adisc.org" under "Global Settings". Make sure that the "Nickname" and the "Nickname (away)" fields contain your ADISC username.
Now, click on the "Lists" tab. Remove any nicknames in the "Nickname List". Once you are done, click on "Apply" then on "OK".