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 I thought, Mozilla stopped syncing to custom servers. I used weave in the past. Does this work again? How about Firefox mobile? At the moment I sync to Nextcloud bookmarks with the Floccus addon in Firefox. Works pretty good.
@mase yes, they discontinued #weave (aka #sync 1.0 or 1.1) because it was too #complex and #unreliable...
now it's sync 1.5! 👨🌾
and it seems to be working well. (though, i didn't test everything, yet...)
with #floccus you can only sync #bookmarks, can't you?
@martin Yes, but bookmarks is enough for me. I don't store tabs or passwords. For passwords I use keepass, which I also sync with Nextcloud. Does it also work in Android?
@mase it is supposed to work on #android, but i can't confirm that...
i'm using #orfox and #fossbrowser, which however do not support sync.
there is no pure #firefox in the @fdroidorg repository (and #google #play #store is not an option). just tried #icecat but cannot sign in to sync (probably related to https://savannah.gnu.org/bugs/?50960)
@mase @fdroidorg thanks! please keep us updated :)
just let me know if you want to use my sync server for temp testing
@martin @fdroidorg I use Fennec from F-droid. Maybe I will give the new sync a try.