Sync with my mobile and all the other devices (4 other computers) is one reason why I use Firefox. It's because it's the only browser, as far as I know, which lets me run my own sync server and offers a open source implementation of it.
Oh neat, when they first switched to sync that wasn't the case (the previous system did allow it over WebDAV and such), but because sync wasn't just a data dump with WebDAV it wasn't possible at launch to run your own server. I'll have to look into that again.
As far back as I remember the code behind sync was on GitHub and I do mean the backend. It probably still is. But I let Mozilla host it cause they encrypt it. If I lose my password I lose my synched items.
It was there I think, but wasn't immediately possible to use a different server as they hadn't enabled or built that into the browser yet. They were still working out issues and I never bothered to check up on it because it seemed like the encryption was secure enough for me.
https://jeena.net/firefox-sync-15