Download ChatZilla from Add-ons
ChatZilla works on the latest versions of SeaMonkey and the Mozilla Suite and versions of Mozilla Firefox up to 56. ChatZilla does not work in Firefox 57 (Firefox Quantum).
ChatZilla is a clean, easy to use and highly extensible Internet Relay Chat (IRC) client, built on the Mozilla platform, which provides all the usual features: multiple servers, a built-in list of standard networks, easy searching and sorting of available channels, logging, and DCC chat and file transfers, plus easy customization with JavaScript plug-ins and CSS styling.