Does anyone know what the exact issue is here? What does Firefox do differently from other browsers?
They make it sound as if Firefox was to blame but don't make it explicit. Could be that they messed and that it has nothing to do with Firefox.
To be fair, "the web" means "what Chrome does" nowadays to a lot of people. Even if it wasn't Firefox's fault but rather some web standard that Firefox adhered to, Firefox will be blamed for not being bug-for-bug compatible with Chrome.