This week in things that never needed a crossover: Friends and Battlestar Galactica!
How far did you make it through this abomination?
An easter-egg in Firefly's pilot episode reveals that it takes place in the same universe as the Alien series. It appears the anti-aircraft cannon Mal uses to shoot down an Alliance fighter was manufactured by Weyland-Yutani Corp.
So does this mean Weyland-Yutani provided the Browncoats with weapons to fight the Alliance? Whose side do you think they were on in the Unification War?