to do so, follow martha's instructions of cutting a 5 7/8" X 6 3/4" piece of felt. but instead of folding the short ends together in the middle, fold the long ends (at least the tissue packs i bought fit better this way) into the middle. measure the around your car's visor and then subtract 6 inches from it (the length of the tissue holder). cut a piece of elastic (i used about 1 inch wide elastic) of that length.
tuck in one end of the elastic (about .5 inch) into one of the short sides, centering it. sew down the side. do the same with the other end. make sure the elastic is on the back side, not the side with the slit opening. you'll have to pull the elastic a bit out so that you don't sew over it in two places.
finished with some embellishments.
and a third one, beaded, but without elastic, just for kicks.