Animated? No. It's already similar to Cowboy Bebop. Lets not go the whole hog.
I've seen a bit of "Cowboy Beebop", and other than some very superficially similar allusions to "old west" themes, I really don't see any similarities between it and "Firefly" at all. One might just as well accuse both of being ripoffs of 1980's "Battle Beyond the Stars" because it featured George Peppard' as a cowboy in a spaceship.