Important caveat with Firefox: You can run your own Firefox Account server (see https://mozilla-services.readthedocs.io/en/latest/howtos/run...) and then e.g. connect to it over a VPN to mitigate a lot of this.

Problem with this is that it needs the sync server:

> Since the Mozilla-hosted sync servers will not trust assertions issued by third-party accounts servers, you will also need to run your own sync-1.5 server.

The tutorial refers to the old unmaintained version: https://github.com/mozilla-services/syncserver, see https://github.com/mozilla-services/syncserver/commit/8d9804...

The alternative is https://github.com/mozilla-services/syncstorage-rs which is ridiculously hard to set up.

https://github.com/mozilla-services/syncstorage-rs/issues/49...

This is the issue to watch, supporting SQLite. This makes it feasible to run a simple sync server for a single user or a small group. But this is not moving forward.