Where's this from
 

A friend of my got a 2010 RX about a month ago, last night when he was cleaning the car he sent me this pic. He found it under his front seat, where did it come from??

I don't know but it looks like a piece of foam. This is use for insulation/noise insulation/vibration shield on many parts of the car. No harm done if not put back.

I found one in mine a while ago too, I didn't know where it was from!

Wiring or adjustment cabling under the seat. This may stop a vibration or rattle should the slack touch against the seat frame. My F150 ( many other cars too I'd guess) has these.