See https://accounts.firefox.com/legal/privacy https://accounts.firefox.com/legal/privacy which links to https://www.mozilla.org/en-US/privacy/ https://www.mozi

See https://accounts.firefox.com/legal/privacy https://accounts.firefox.com/legal/privacy which links to https://www.mozilla.org/en-US/privacy/ https://www.mozilla.org/en-US/privacy/ But in practical terms, I am not aware of any uses of the sync data apart from actually syncing it. That is, no mining of that data, etc.