Ford's first response to my question on 11/2/99:
"To determine if the Michelin LTX M/S P235/75R15 tires would be an
acceptable substitute for your Stock Firestones, it is recommended that
you contact the tire manufactures directly because they are in the best
position to address your inquiry. "
Ford's Second response to my question on 11/2/99:
"After further research, the Owner's Manual states that you must make
sure that all replacement tires are of the same size, type,
load-carrying capacity and tread design (e.g., "All Terrain", etc.), as
originally offered by Ford. Do not replace your tires with "high
performance" tires or larger size tires."
Well, if this is true, then the Michelin LTX P235/75R15 M/S should be fine, because the stock Firestones are P235/75R15 M/S. Could it be that Michelin received the same advisory from Ford (out of the Manual), looked at the Fstone Wilderness AT tires, thought the AT meant all terrain (which we know it DOES NOT, these tires are marked M & S), which would lead Michelin to advise using their A/T all terrain version of the LTX? As noted by MikeP above, the LT in LTX creates confusion, since LTX is available in "P" or "LT". Ford may look at the LT in LTX and say, not approved since they may believe it to be light truck, not passenger rated.
I think Ford is just looking for a way to void your warranty on anything tires may affect.
To answer the question of price, I found the A/T version of the LTX is less money than the M & S.