“Why does Thunderbird look so old?” That’s one of the most frequently asked questions about Thunderbird, according to Thunderbird Project Design Manager Alessandro Castellani (along with “Is Thunderbird dead?”). And it’s one he seeks to answer definitively in a new blog post about Thunderbird’s planned 2023 release, codenamed Supernova.

Source: Mozilla plans ground-up UI redesign for Thunderbird email client this July