Lori,
Mountain Lion 10.8.x does NOT use Safari 5.x It uses Safari 6.x and for the latest update of Safari on Mountain Lion, Mac OS X 10.8.3 and Lion, Mac OS X 10.7.5 the update version is Safari 6.0.4. The Safari 5.1.9 issue you are referring to in your post ONLY impacts users of Mac OS X 10.6.x, Snow Leopard.