Things will get sorted out as you go along. GR is a generalization of SR to non inertial reference frames, so it does contain this explanation, but we normally speak of SR as the theory that explained the failure of M&M to detect the ether, at least in the sense that SR predicts their results without assuming assuming the existence of an ether.
Physicists do seem to get more than their share of those moments, but fortunately they're nice enough to share a few of them with us.