Relax! I went for a interview at toys'R'us in uk , the manager was relaxed it was very informal just like talking to a freind!
Of course they could all be run different , but brush up on some interview questions online , theres nothing worst then being asked "what do you know about our company" and being like "DERP U SLL TOYS".....
Something better would be to research there company , mention any recent expansion of the company ect. Also at the end of the interview they will ask you if you have any questions. ALWAYS have a question trust me it helps to show interest in the company like this.
Otherwise remember to sell yourself and they need you as much as you need them , they just want to make sure you are capable and not a freak.