This isn't for me, obviously but a friend of mine has an early 4Runner that has some headliner with some major self-esteem problems. It's not typical carpet either, it's more like a closed-cell foam material, and whatever adhesive was on the backing has deteriorated over 20 years under a black roof.

What would you guys recommend for adhesives?

Any auto parts store will have a 3M headliner adhesive spray. This stuff is perfect. I will caution you though, if the foam backing is the part which has deteriorated, it will NOT bond again. He is forced to buy new material and redo the entire thing.

If there is a foam backing, run your hand across the foam and see if any of it flakes off. If it does, the foam needs to get replaced. The foam and not the adhesiveis usually the problem and in a 20 year old vehicle, it's more likely that the foam has just bit the dust. Good Luck!!!