很久以前就不推荐使用getYear()这个函数，因为在火狐中显示是不正确的，推荐使用getFullYear() 函数。
另外火狐不支持innerText这个属性，需要改为textContent才能接收。
然后附上代码
var s,Sys = {},ua = window.navigator.userAgent.toLowerCase();
(s = ua.match(/msie ([\d.]+)/)) ? Sys.ie = s[1] :
(s = ua.match(/firefox\/([\d.]+)/)) ? Sys.firefox = s[1] :
(s = ua.match(/chrome\/([\d.]+)/)) ? Sys.chrome = s[1] :
(s = ua.match(/opera.([\d.]+)/)) ? Sys.opera = s[1] :
(s = ua.match(/version\/([\d.]+).*safari/)) ? Sys.safari = s[1] : 0;
//浏览器版本号进行测试
//if (Sys.ie) { document.write('IE: ' + Sys.ie); }
//if (Sys.firefox){ document.write('Firefox: ' + Sys.firefox);}
//if (Sys.chrome){ document.write('Chrome: ' + Sys.chrome);}
//if (Sys.opera){ document.write('Opera: ' + Sys.opera);}
//if (Sys.safari) { document.write('Safari: ' + Sys.safari); }
var today = new Date();
var day,date;
if (today.getDay() == 0) { day = " 星期日"; }
if (today.getDay() == 1) { day = " 星期一"; }
if (today.getDay() == 2) { day = " 星期二"; }
if (today.getDay() == 3) { day = " 星期三"; }
if (today.getDay() == 4) { day = " 星期四"; }
if (today.getDay() == 5) { day = " 星期五"; }
if (today.getDay() == 6) { day = " 星期六"; }
date = "今天是：" + (today.getFullYear()) + "年" + (today.getMonth() + 1) + "月" + today.getDate() + "日" + day + "";
if (Sys.firefox)
{
document.getElementById('time_id').textContent = date;
} else {
document.getElementById('time_id').innerText = date;
}
