Most of the content on support.mozilla.com was written by volunteers. In addition to this website, the Mozilla Community includes many developers and long-time Firefox users who run other Firefox support resources. This page lists several websites and other venues for Firefox support, that are worth checking out.
To access IRC, you'll need an IRC client: if you don't have one, you may want to install the Chatzilla extension for Firefox. Just click on "Install," authorize the installation, and restart Firefox.
Once you have a client, you can talk to other users in real time by joining in the #firefox channel on irc.mozilla.org (Mozilla's chat server). (If you're using Chatzilla, clicking the link above should open a new window. Simply type your question in the text field which appears next to your nickname at the bottom of the window, and wait for an answer).