JPEG XL had so much going for it. Kinda sad it was killed off just like that.
replies(7):
On the web alone it should be close to a billion users with support for JXL due to Safari’s market share.
[1]: https://cloudinary.com/blog/jpeg-xl-how-it-started-how-its-g...
But if you go getfirefox.com, click "Download Firefox" then there will be no JXL support not even behind any configuration flags. So no, it doesn't support it. There are also no plans to enable support with the current implementation.