In one form or another, Firefox Sync has been around for years (in fact, it's not that far off being decades...).
It allows you to share tabs, history and bookmarks between browsers on different devices (though, frustratingly, it doesn't sync settings or extension config).
Although sending that data via a 3rd party server might sound concerning, Mozilla are unable to see the content that's being synced because the data is end-to-end encrypted.
All the same, I like to self host where possible (and, frankly, needed something to keep me out of trouble), so decided to look at the feasibility of self-hosting a sync server.
This post talks about the process of setting the sync server up: it's been tested as working...
