More relevant to Firefox than Thunderbird, perhaps, but the advantage to using web technologies for their own front end is that it forces them to eat their own

More relevant to Firefox than Thunderbird, perhaps, but the advantage to using web technologies for their own front end is that it forces them to eat their own dogfood at least. Given that Mozilla wants the web to win, making sure their platform is well-rounded enough to performantly build their own products on top of seems like a wise strategy. Kind of a vote of no-confidence otherwise.