[TingPing]

Firefox Sync is somewhat open. The service is foss and third-party browsers implement it.

[sph]

Which third party browsers? Epiphany does, but it's not a very good browser, sad to say, and pretty much noone uses it.

[TingPing]

Epiphany and Eolie.

I guess your point is Mozilla would care if they were bigger. Nobody can say. The service documents you are allowed to use it as long as you don't use Firefox/Mozilla branding.