Burning Oil??

Hello, I recently had my car in for brakes/rotors. Firestone replaced all 4 rotors and brakepads and also changed the air filter. Soon after that, everytime I switch the car off, I smelt oil for a couple of mins. I am not sure what is wrong, since I am not an expert in this at all. Thus was wondering if anyone can advice me as to what the problem might be.
Also another thing is that everytime I switch on the AC it blows some stinky air and then its fine. Any clues for that?? Any help would be appreciated!!!
Thank you