FIG. 1 is a top/front/left side view of the firearm support brace of our invention; FIG. 2 is a top/rear/right side view of the firearm support brace; FIG. 3 is a rear view of the firearm support brace; FIG. 4 is a right side view of the firearm support brace, the left side view being a mirror image thereof; FIG. 5 is a top view of the firearm support brace; and, FIG. 6 is a bottom view of the firearm support brace.