The writers give Alan Tudyk an opportunity to say hello to some old friends midway through S1 Ep7, “Van v Emily: Dawn of Justice” (link is to episode playback at NBC.com).
It comes near the top of Act 3, roughly at the 14:30 mark.
This post was originally published as "Firefly shout-out in recent episode of Powerless on NBC." by What Would Malcolm Reynolds Do? at Whedonesque