We claim the ornamental design for a firearm upper receiver, as shown and described.
FIG. 1 is a rear perspective view of a firearm upper receiver according to one embodiment of the present invention.
FIG. 2 is a front perspective view of the firearm upper receiver of FIG. 1.
FIG. 3 is a right-side view of the firearm upper receiver of FIG. 1.
FIG. 4 is a left-side view of the firearm upper receiver of FIG. 1.
FIG. 5 is a top view of the firearm upper receiver of FIG. 1.
FIG. 6 is a bottom view of the firearm upper receiver of FIG. 1.
FIG. 7 is a rear view of the firearm upper receiver of FIG. 1; and,
FIG. 8 is a front view of the firearm upper receiver of FIG. 1.
The portions of the firearm upper receiver shown in broken lines are included for the purpose of illustrating environment and form no part of the claimed design.