The right side mirror on my GX does not adjust horizontally anymore. I am not sure if the 4Runner is a similar design, but has anyone else seen this happen? I was cleaning the surface when the mirror turned out. I adjusted it back into position, but now it only adjusts vertically.

 

I remember something similar on my Land Cruiser with a like design. I'm assuming we're talking about the glass mirror and not the plastic mirror enclosure. Try centering the glass in the middle of the motor travel manually by adjusting (the ratcheting sound won't hurt anything) to mid-way horizontally, then try the switch adjustment method again. I'd accidentally moved it to one extreme while washing and got it off-track or something. Otherwise, if you're just beyond warranty, ask the selling dealer for a "policy adjustment" = free.

And welcome to YotaTech!