var is_opera =  navigator.userAgent.indexOf('Opera') > -1;
var is_safari = navigator.userAgent.indexOf('AppleWebKit/') > -1 && navigator.userAgent.indexOf('Chrome') == -1;
var is_chrome = navigator.userAgent.indexOf('Chrome') > -1;
var is_firefox = navigator.userAgent.indexOf('Firefox') > -1;
var is_mac = navigator.platform.toLowerCase().indexOf('mac') > -1;
var is_linux = navigator.platform.toLowerCase().indexOf('linux') > -1;
var ie6 = false;
var ie7 = false;
var ie8 = false;
var ie9 = false;