The comic books are "inbetweenquels" that flesh out the mythology between certain events. I can't say more without spoiling it, but there is a reason the show can do comic books without most of the main cast. I doubt Serenity would ever have gotten greenlit if only one or two members of the Firefly cast were in it and the movie didn't really focus on them.

You need to see the show and put it in your queue as soon as possible. There are only 26 episodes so you should get through it fairly quickly regardless.