[Q] Firefox-Account, where does it come from? topic

It's only a very short question. The last days I was thinking about that thing. If you go to "Accounts" you'll see, that you can register a Firefox-Account. I want to know, which apk provides that functionality, because I haven't found anything. It's not the big impoertant wuestion, but I bothers me also. Maybe someone knows the answer.
Thanks in advance.