XUL was HORRIBLE to write, implement, and debug. Been there, done that. It was also 0% portable.
WebExtensions (even if there are some technical limitations and some browser manufacturers decided to intentionally cripple some of the APIs) are in general so much better. You have proper toolchains for development, translations, testing, and publishing. And it is pretty much portable to all browsers. You don’t even have to port anything 99% of the time because it’s just compatible.
XUL was HORRIBLE to write, implement, and debug. Been there, done that. It was also 0% portable.
WebExtensions (even if there are some technical limitations and some browser manufacturers decided to intentionally cripple some of the APIs) are in general so much better. You have proper toolchains for development, translations, testing, and publishing. And it is pretty much portable to all browsers. You don’t even have to port anything 99% of the time because it’s just compatible.