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.
It's more the general tone than any specific "allusions to 'old west' themes" (Bebop was noir and blues, not western and country, anyways). It's hard-on-their-luck bounty hunters looking for jobs on the various terraformed planets and moons in one solar system, occasionally being Big Damn Heros, but normally getting screwed, instead of Firefly's hard-on-their-luck bounty huntees looking for jobs on the various terraformed planets and moons in one solar system, occasionally being Big Damn Heros, but normally getting screwed. They also both have a similar mix of humor and serious business.
While they aren't the same, Cowboy Bebop is the closest thing to an animated Firefly there is.