Thank you for pointing that out, I don't use the sync feature because I don't like giving too much info to 3rd party services but I never considered running it on one of my servers.

I've just skimmed through this guide: https://docs.services.mozilla.com/howtos/run-sync-1.5.html#h...

It doesn't look too difficult and it says that running your own account server is optional. Or does it mean that you can run your own sync server using a mozilla account? I'm not sure I understand how sync server and accounts server interact exactly...