[redxblood]

What? Firefox doesn´t do that unless you explicitely create a firefox sync account, I don´t know about chrome

But if you are talking privacy, I assure you Firefox is 10x better in pretty much every aspect.

[muhammadtaqi]

What if we sync account on Firefox, how much Firefox use our data?

[bzbarsky]

See https://accounts.firefox.com/legal/privacy which links to 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.