We claim the ornamental design for a folding rooftop carrier, as shown and described.
FIG. 1 is a perspective view of a folding rooftop carrier;
FIG. 2 is another perspective view of a folding rooftop carrier;
FIG. 3 is another perspective view thereof;
FIG. 4 is front elevational view thereof;
FIG. 5 is a rear elevational view thereof;
FIG. 6 is a left side elevational view thereof;
FIG. 7 is a right side elevational view thereof;
FIG. 8 is a top plan view thereof; and,
FIG. 9 is a bottom plan view thereof.
The dashed lines in FIG. 1 illustrate environment only. The broken lines in the Figures illustrate unclaimed portions of the folding rooftop carrier and form no part of the claimed design.