Continuity mistake: In episode 64, "For Whom The Bell Tolls. And Tolls. And Tolls", Tracy is shown seated at the table with a bowl of cereal - but in the shots immediately before and after, she's not there, nor is there any food at her place. (00:01:10)
Audio problem: Billie says her line "he needs a new image" without moving her lips.
Firefly, Light My Fire - S1-E1
Revealing mistake: Courage winces and reacts before the stereo-zapper is fired.