Kramer (Michael Richards) fulfills his dream of being the ladder man for a fire company. The Firehouse that the firemen reside at is the firehouse that was used for exterior shots in both Ghostbusters (1984) and Ghostbusters II (1989).
We find out that the J. in J. Petermen's (John O'Hurley) name stands for Jacobo. We also find out he grew up in Costa Rica.
From the outside you can see the restaurant where Peterman (John O'Hurley) meets George (Jason Alexander) & Jerry (Jerry Seinfeld) is the same restaurant used in episode 2.11, The Chinese Restaurant (1991). The inside is different however.
The dialogue coach for the series, Judy Kerr, has an uncredited appearance as a woman in the street who asks Jerry (Jerry Seinfeld) how the fire began.