From looking at the diff, it seems to be in the same vein as the IRC, XMPP, Google Talk(!), and some weird network I've never heard of "Odnoklassniki" (https://en.wikipedia.org/wiki/Odnoklassniki)

https://support.mozilla.org/en-US/kb/instant-messaging-and-c...

So, in other words: it merely expands the already shipping chat clients to be just one more

Fair enough, I guess. I never realized Thunderbird already supported those. I always had HexChat, Pidgin, or Fractal for IRC/GTalk/Matrix at the ready instead.

It has a good (at least for my purposes) RSS reader, too, which is actually my primary use for it lately

https://support.mozilla.org/en-US/kb/how-subscribe-news-feed...

Thunderbird supports irc?

It's called Chatzilla, it's not great nor widely used.

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].

[1] https://i.imgur.com/LQrzpoy.png

[2] https://i.imgur.com/X8idAGl.png

[3] https://bugzilla.mozilla.org/show_bug.cgi?id=1618061

It's been a chat client for such a long time that I think it makes sense to add Matrix support, which is a much more modern protocol than the others supported. I think we've all just forgot that it has chat features, since it only supported protocols like Google Talk, IRC, and XMPP.

Thunderbird also has support for Usenet out of the box. I think the product sees itself more as a complete communication program than just an email program, even if that is what most people use it for.

Chat came to Thunderbird for free - it was developed by a different team and they offered to integrate it, and did so.

This is great for users who are looking for unified communications. Further, chat sessions are index searchable if the user has enabled it.