The ornamental design for a firesprinklerheadguard, as shown and described.
FIG. 1 is a front perspective view of the fire sprinkler head guard showing the new design, the rear perspective view is a mirror image of the illustrated front perspective view;
FIG. 2 is a rear plan view of the fire sprinkler head guard showing the new design, the front plan view is a mirror image of the illustrated rear plan view; and,
FIG. 3 is a left side view of the fire sprinkler head guard showing the new design, the right side view is a mirror image of the illustrated left side view.
The broken line showing of environmental structure is included for the purpose of illustrating and forms no part of the claimed design.