[crapple8430]

Firefox sync clearly requires a central server. For any kind of peer to peer syncing to work you must have the machines on at the same time and accessible. And then there is the issue of NATs, including CGNATs. To work reliably these almost always have to have some kind of relays anyway (Tailscale's DERP, Syncthing also has relays).

For the experience an average consumer expects, you at a minimum need a central short-lived cache.

[allan_s]

Yes sorry I meant firefox not for the way its sync , but in the way its a heavy client you install. As said for me most of my devices will be at some times during the week in the same nat so that no centralized server even short lived should be needed. And for personnal use, I only care if the device I have on me is the one with latest data especially as for most use case I'm the only one reading/ writing , so eventually consistency is not an issue