It's been many years since Firefox dropped support for XUL extensions and XUL itself. It even lead to Firefox being forked, and Palemoon browser (amongst other forks of it) now carry the legacy of XUL ( https://udn.realityripple.com/ ). Also, that hasn't stopped Firefox from offering stand alone Gecko on Android ( https://mozilla.github.io/geckoview/ ) now, has it? If they can do it for Android, why not all the other desktop platforms? Start redirecting the 300+ million dollars they have earned from Firefox to the developers instead of the CEO et al and maybe we will see some good innovation happening in Firefox ...