12/20/2007 (09:30PM - 10:00PM) (Thursday) : The gang at "30 Rock" returns from their summer hiatus. Liz's (Tina Fey) excitement to be back and see Jack (Alec Baldwin) is quickly squashed when he tells her that despite what she thinks, she is not over Floyd. Jack also tells her about his plan for SeinfeldVision, which entails using NBC-owned footage from Seinfeld's show and inserting him into NBC's current shows. Jerry Seinfeld (Guest Star Jerry Seinfeld) shows up at Jack's office upset about SeinfeldVision. Meanwhile, Jenna (Jane Krakowski) has gained weight over the summer after doing the musical, "Mystic Pizza: The Musical!" and Kenneth (Jack McBrayer) becomes Tracy's (Tracy Morgan) office wife when Tracy's wife kicks him out. Jerry Seinfeld guest stars; Lonny Ross, Judah Friedlander, Scott Adsit, Keith Powell, Katrina Bowden and Maulik Pancholy also star.