The ornamental design for a firearmrearsight, as shown and described.
FIG. 1 is a perspective view of a firearm rear sight showing my new design;
FIG. 2 is a left-side elevation view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a right-side elevation view thereof;
FIG. 5 is a rear elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is bottom plan view thereof.
The broken lines and the areas within them depict portions of the firearm rear sight that form no part of the claimed design. The dot-dash-dot broken lines in FIG. 6 form a boundary of the claim and form no part thereof.