On the Blu-ray discs
Firefly has a picture that's a little softer than most Blu-ray discs (especially in the effects shots), but it is an improvement over the DVDs (even in an upconverting DVD player or Blu-ray player), and the punchy sound (DTS HD 5.1 compared to the DVDs' 2.0 surround) is a definite upgrade. In addition to the original bonus features, there are a couple new ones: a 25-minute conversation among Whedon, Nathan Fillion, Ron Glass, and Alan Tudyk in which they discuss the series and a number of specific episodes (Fillion recalls thinking he was getting fired after the first episode), and a new commentary track by the four fellows on "Our Mrs. Reynolds." And since it's easy to get sucked into watching multiple episodes, it's nice to have a Play All feature on the BDs.