Not only that, but syncserver can be locally installed so you have an additional layer of autonomy if you want that. (The data itself is already end-to-end encrypted, so it is not really necessary to be exact.)

Here is the repo for reference:

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

One of Firefox's best features, works seamlessly across 5 devices.

Used this for a while and it works well. Sounds like what the OP wants, as well.

came to say this. Simple, effective.