Third edition replaced the cardboard standees with plastic miniatures of the "mechs". It also lost the nicer cardstock maps, and replaced them with paper maps. The game was still a complete playable set right out of the box, but many more supplemental materials were available by this time to expand the universe, including CityTech and AeroTech boxed game sets and technical manuals.
FASA released the third edition in 1992 in a standard FASA box size, or "thin box" edition; third edition was then re-released in 1994 in a larger "thick box" edition that was identical other than being in a thicker box - the same size box as FASA releases like Solaris VII. The contents were identical in both editions.