There is a plug-in for Firefox to provide irc, called chatzilla. This is simple to install in Firefox. First ensure you have Firefox installed. Then find the chatzilla plug-in in the mozilla addons page - just search for chatzilla. Don't pick the French language one by mistake (unless you want French!). Just click to install and confirm.
Once you have installed, just type irc://irc.z.je/hubs in to Firefox location bar (where you type a web page). That will open the chatzilla window and join the HUBS chat channel. You will want to type /nick followed by a suitable nick name that you want to use. You can use irc://6.irc.z.je/hubs instead if you have IPv6.
Instructions for IRC shamelessly adapted from Andrews & Arnold