The short answer is yes, because the film supposedly stands alone even if you haven't seen the series. (I've read quite a few reviews by people who either hadn't seen the series or had non-Firefly fans with them, and they all seemed to enjoy the movie.)

But if you like it, you'll probably want to watch the TV series afterwards, just to get more background on the characters (because of course they can fit more characterization and the like into a 13-hour TV series than into a 2-hour movie).