The ornamental design for an ironing board foot extender, as shown and described.
FIG. 1 is a perspective view of an ironing board foot extender showing my new design, the broken lines showing an ironing board and additional foot extender being for illustrative purposes only and forming no part of the claimed design;
FIG. 2 is an enlarged top left perspective view of the foot extender;
FIG. 3 is a top front perspective view of FIG. 2;
FIG. 4 is a top rear perspective view of FIG. 2; and,