Peel and segment the grapefruit and orange, removing all the white pith. Cut the citrus segments into ½-inch pieces and place them in a large mixing bowl. Peel and dice the mango, seed and mince the jalapeño, and mince the cilantro; add them to the bowl. Squeeze the juice of the lime into the bowl, add the salt, and toss with two wooden spoons for a full minute. Taste and adjust seasonings.