Headrests are in the Boeing Master Minimum Equipment List listed in section 25-21-5 and are a C item (10 days) and need to be installed.
However, even my airline removed this part from the CAA-approved MEL very silently, thus you may not even find it.
This is illegal and unacceptable.
They (headrests) help and improve to do the mandatory overhead panel check inflight....
