The cult sci-fi drama was axed by Fox after just 14 episodes, but was later revived by Avengers director Whedon for 2005 film Serenity.
"It's something I would love to do," Whedon told the Toronto Sun of a second Firefly movie.
"Part of me is like, 'God, it would be great when I finish Avengers 2 to do [a sequel]'."
The writer/director said that he would "never really accept" that Firefly is over for good.
"I always, in the back of my head, think, 'What if I could get the old gang back together?'," he admitted.
Firefly star Sean Maher - who played Simon Tam - recently voiced his support for a sequel to Serenity.
"A television show would be very tricky with all of our availability, and I don't think that's in the realm of possibility," Maher said in November. "But what about another movie?"
> Firefly: Tube Talk Gold
Watch Nathan Fillion talk Firefly and Joss Whedon with Digital Spy below: