The ornamental design for a detachably mounted headrestraint, as shown and described.
FIG. 1 is a left front perspective of a detachably mounted head restraint, showing my new design;
FIG. 2 is a top plan view, thereof;
FIG. 3 is a front elevational view, thereof;
FIG. 4 is a rear elevational view, thereof;
FIG. 5 is an elevational view of one side, the opposite side elevational view being a mirror image, thereof;
FIG. 6 is a bottom plan view, thereof; and,
FIG. 7 is a perspective view taken to a reduced scale.
The broken line representations of the head and shoulders of a person, the portion of a seat and headrest, and the attachment straps shown in FIG. 7 are included solely for illustrative purposes, forming no part of the claimed design.