I use Firefox as my primary browser, and I would absolutely love to be able to use the Firefox Sync functionality to sync bookmarks, etc. across several devices.

However, I do not want to risk storing absolutely sensitive data (browsing history, auth cookies, credentials, etc) at some third party.

Everytime this comes up in HN comments, someone says that Firefox Sync can be self-hosted. And while this was true in the older versions of Firefox, it seems to me that self-hosting is currently neither supported nor documented. And it has been like this for at least since 2020[1][2].
It seems self-hosting is not a priority for Mozilla.

Is anyone actually self-hosting Firefox Sync?
If so, how do you do it?
How is it working for you?
Any issues to be aware of?

[1]: https://github.com/mozilla-services/syncstorage-rs/issues/681
(opened on Jun 22, 2020)

[2]: https://github.com/mozilla-services/syncstorage-rs/issues/550
(opened on May 26, 2020)