just setup a private #firefox #sync server. pretty straight forward... 
1. build a #docker image from https://github.com/mozilla-services/syncserver
2. #deploy it somewhere
3. configure identity.sync.tokenserver.uri in #about:config to point to your new location
4. login at `about:preferences#sync` (you still need a #mozilla account, unless you also run a private account server)
5. sync and check about:sync-log for #error|s
@martin Should also add that elementary OS's native browser, Epiphany (based on Gnome Web), syncs with Firefox accounts—so you don't even need Firefox, technically!
(IMHO Epiphany is a totally decent browser if you don't need a ton of extensions—comes with built-in adblock, lighter than Chrome & Firefox.)
@nev but i can't figure out how to point #epiphany to my private #sync server...!?
the settings seem to be #hardcoded..?
https://gitlab.gnome.org/GNOME/epiphany/blob/master/lib/ephy-sync-utils.h#L33
do you have any #experience with that?
@martin it uses your Firefox account, so yeah, it syncs with both FF & Epiphany. E. g. when sharing a link via Firefox mobile I can send it to Firefox desktop, or Epiphany.