I don’t know how it actually went down, but since it’s open source software the Matrix integration could have been written by a random developer who doesn’t work for Mozilla.

Thunderbird has been more than "an email client" for so long that people made the exact same kind of complaint when RSS support was added.

Thunderbird is a messaging/communications client, and way more people will benefit from Matrix support than would ever benefit from Maildir support.

Further, my understanding from the Thunderbird team's comms is that they are very much in control of their own destiny. I don't get the sense that Mozilla has much say in Thunderbird's roadmap (or even cares) at this point.

> but adding chat functionality is higher priority?

Absolutely yes. Maildir support is a niche want, where as chat has become essential for many offices replacing email for most internal communication.

Additionally the chat fuctionality has been available in one form or another for years but has been quite neglected. They have just finally extended it and cleaned it up

Surely there is a Matrix to Maildir thing or something you can use, now that it supports Matrix. Duh. /s