Review for ChatZilla by le Cauchemar
Rated 5 out of 5 stars
I chat via IRC nearly the whole day and really like this client.
It looks nice and configurating it is quite simple.
By using an add-on to split the browser window, it can also be started in a sidebar.
The only negative thing about it: if you have to restart Firefox (for example if after (de)installing/activating an add-on or if there's a problem while browsing), the client is closed with the browser :(
To create your own collections, you must have a Mozilla Add-ons account.