air filter box is held in by two "clips"

just push down on the box and it should snap into place

if you pull it all the way out you will see where it clips in, it is in the area of the transmission mount

- 95 Mystique LS - Zetec/5spd - 99 Contour SeVT Sport - Duratec/5spd Official NE-CEG Contour/Mustang Family