There is only XUL!

Long dead. Now there is no XUL, only (private user) data (that Mozilla sells for revenue)

I think they're making a Ghostbusters joke, btw

Mozilla made the joke themselves, about Firefox. "There is no data, there is only XUL" was an official XUL catchphrase. But now there is no XUL, and Mozilla sells private user data, so it's reversed.