The ornamental design for a firearm, as shown and described.
FIG. 1 is a top, front, left perspective view of a firearm showing our new design;
FIG. 2 is an enlarged fragmentary top, front, left perspective view thereof;
FIG. 3 is an enlarged fragmentary left view thereof;
FIG. 4 is an enlarged fragmentary right view thereof;
FIG. 5 is an enlarged fragmentary top view thereof; and,
FIG. 6 is an enlarged fragmentary bottom view thereof.
The uneven-length broken lines immediately adjacent to the solid line disclosure represent the unclaimed boundaries of the claimed design. The even-length broken lines showing the remainder of the firearm are for illustrative purposes only and form no part of the claimed design.