This resulted in more than just a bit of confusion on my part, not being a FireFly fan or having any clue what was going on. Dori to the rescue, though, a self-professed FireFly fan-girl: they’re the same thing. “Fox cancelled the TV show, and Universal picked it up as a movie.” Thanks, Dori, that explains it.
Aaahh. I suppose there’s some logical reasoning, but a simple “Serenity. The movie that continues where FireFly left off” banner would have helped a lot, methinks.