Facebook could try to counter Chrome with Facebook integration in IE, but it wouldn’t be the game-changing move Facebook needs to put Google on the defensive. The only way Facebook can knock Google off its feet is to build its own browser and use its massive reach to promote it.
Currently there is a similar threat to smartphone camera applications by Instagram, who doesn’t get bundled with the users but the most engaged photographic content is still at Instagram because of the window they provide to the social graph.
Browser stats & extensions has nothing to do with where my 229+ other friends are, as well as 50+ photo albums. So it doesn’t matter what medium users interact with your service as they develop a heritage of usage and create connections with whatever matters to them during that time.