Let me know what you find out, I have used Xfire myself many moons ago. If not request them to add DCS World! Their team works really hard to add all games, I suppose no one requested DCSW from them yet.
Some people don't know, but great thing about Xfire it was "out-of-DRM experience ala Steam", and you could see what your friends are playing and join directly to their servers. Also, if game was "full-screen" only, you could still bring it on top and chat. Since Xfire inception in 2003 it still is being developed and has over 20milion users and over 2000 games supported. Although it was never really a lobby dedicated for flight sims I believe, it did list DCS:BS1 http://social.xfire.com/games/dcsbs