var url = gBrowser.currentURI.spec; if (!url.match(/(\d+)(\D*)$/)) throw "No numeric value in URL"; var num = RegExp.$1; var digit = (num.charAt(0) == "0") ? num.length : null; num = parseInt(num, 10) + aIncrement; if (num < 0) throw "Cannot decrement number in URL anymore"; num = num.toString(); digit = digit - num.length; for (var i = 0; i < digit; i++) num = "0" + num; loadURI(RegExp.leftContext + num + RegExp.$2);