On the contrary; Thunderbird's chat has built-in IRC support which you can use without installing something like ChatZilla [1][2].
It's not very good, though, including warts such as automatically attempting an SASL login with your credentials, even if you've never registered a services account on the IRC network [3].
It's not very good, though, including warts such as automatically attempting an SASL login with your credentials, even if you've never registered a services account on the IRC network [3].
[1] https://i.imgur.com/LQrzpoy.png
[2] https://i.imgur.com/X8idAGl.png
[3] https://bugzilla.mozilla.org/show_bug.cgi?id=1618061