Firefly IS worth watching IMO even knowing how it pans out cancellation-wise. The movie does a credible job of wrapping things up, even if it can't provide the multi-season arc we would have wanted.

It did start out slightly slow before becoming awesome, but yes you should avoid it. Although it was awesome, they cancelled it at a pretty gigantic cliffhanger in both the main plot and (surprisingly compelling) romance plot. I got to the last episode knowing it was cancelled and was so upset I wished I hadn't watched it.

Edit since I see now there may be some ambiguity - my comment here is specifically regarding Outcasts, not Firefly. I don't think (or didn't see) the Firefly reference was there before their edit.

That image hurt me.

That looks interesting, but based on the fact that I'm still talking about how I couldn't handle the cliffhanger cancellation of Outcasts, I think I will give it a miss.