How should a postdoc address senior research staff and faculty members in the USA?
When I was a grad student, my initial preference was to call faculty "Doctor" or "Professor".  At some point (about halfway through, I think) one professor said to me: "If you want them to see you as a peer, you should call the professors the same way that they call each other."  At my university, all the professors called each other by their first names (it didn't matter if they were assistant, associate, or full).  Since I planned to make a career in academia, I really did want to be viewed as a peer.  So I started calling them by their first name (and no one ever told me to do otherwise).