Continuity mistake: In "Firewalker," Mulder reports that the day is November 11 and that he and Scully ended up in a 30-day quarantine. Scully reports that the date for the autopsy in "Irresistible" is November 14, which conflicts with the quarantine.
Visible crew/equipment: Near the beginning, Mulder, Scully, and another man are walking through a graveyard. The camera is following them to the right passing head stones. The crew can be seen reflected in a black shiny head stone as the camera passes.