If there’s one thing that reinforces the expectation that BigCorp controls my data, it’s a login like this:
You can use your own sync server if you are prepared to configure the sign-in procedure like this:
To configure desktop Firefox to talk to your new Sync server, go to “about:config”, search for “identity.sync.tokenserver.uri” and change its value to the URL of your server with a path of “token/1.0/sync/1.5”:
That’s if you ever guessed it was possible and went looking.
I would love to see Firefox promote owning one’s own identity and data, by prominently displaying the option to use one’s own server. An example from Matrix: