Firefly was rated TV14.
Assuming this question is supposed to be... "What are the ratings for Family Guy's Star Wars episodes"?, the rating was and is most likely the same as the show is always rated, TV14. You should research it online to be sure.
Firefly was rated TV14 at the time, which means material in the show is unsuitable for children under 14 years old.
Your question makes no sense, if by chance you're asking what it's rated, that would be TVPG occasionally TV14
The rating is R.
It is rated TV14 (in the U.S.) so it's recommended for ages 14 and over. Naturally it would be up to the parents to decide if they wanted their children to watch the show, of course nowadays, kids can easily find a way to watch it regardless of their parent's wishes.
The Cosby Show
We Stole the Show Brooklyn's Finest - 2013 was released on: USA: 12 February 2013 (internet)