> a fully open source GPL licensed, self-hostable, webmail server application that fulfills the same functions as rainloop or roundcube, implemented in the Thunderbird name. Maybe it could have its own new GUI to run inside the browser, or it could offer an optional "traditional" GUI that is similar to the Thunderbird desktop client. This has a possibility for a natural symbiotic relationship with Firefox, as the best and most optimal web browser client to view the webmail.

If this shares neither the thunderbird feature set or UX, why does it have to be called thunderbird? I still use thunderbird because it's UX efficiency for dealing with large volumes of mail blow away the Gmail and Fastmail web interfaces.