Use this timeDifference(new Date(), new Date().setTime(Date.parse("2013-05-13T13:12:42.000Z")))
If you have a problem with the "(ISO 8601)" part, use this timeDifference(new Date(), new Date().setTime(Date.parse("2013-05-13T13:12:42.000Z (ISO 8601)".replace(/ *\(.*\)/,""))))