<…> privacy minded person installs <…>

That’s the fallacy. You assume all Firefox users are privacy minded. Which is idealistic, not a reality. From Firefox being pre-installed on Linux to Mozilla themselves marketing it the opposite way.

Who is at fault here, the application or the user?

There is no universe where opt-out tracking is not abusive behavior. Literally, read the Mozilla blog and see how they used to condemn this same behavior before.