Yeah, that last chest (in the fire area, near that superfluous bridge at the end of the river) contains the Wild Dweller Leggings. To get it, you can drink a potion or cast Healing (if you have it), then hope the regeneraton outpaces the fire damage.
Also, jumping into the river instantly removes the fire status, so that's a last ditch effort.
There are two other chests in that fire area of the Temple of Doom, but they contain nothing special, and are MUCH harder to reach without dying.
