网页在手机上自动缩放100% 适配safari firefox 安卓原生浏览器

<head><title>我是 title</title>
<script>
    function myBrowser(){
    var userAgent = navigator.userAgent; //取得浏览器的userAgent字符串
    var isOpera = userAgent.indexOf("Opera") > -1;
    if (isOpera) {
        return "Opera"
    }; //判断是否Opera浏览器
    if (userAgent.indexOf("Firefox") > -1) {
        return "FF";
    } //判断是否Firefox浏览器
    if (userAgent.indexOf("Chrome") > -1){
  return "Chrome";
 }
    if (userAgent.indexOf("Safari") > -1) {
        return "Safari";
    } //判断是否Safari浏览器
    if (userAgent.indexOf("compatible") > -1 && userAgent.indexOf("MSIE") > -1 && !isOpera) {
        return "IE";
    }; //判断是否IE浏览器
}
var mb = myBrowser();
var chengfa = 1;
if("Safari" == mb){
chengfa = 1;
}
if("Safari" != mb){
    if(window.orientation == undefined){
        document.write("<meta id=\"viewp1\" name=\"viewport\" content=\"width=1400px, minimum-scale=0.1,maximum-scale=2.0, initial-scale="+(window.screen.width * 8/(chengfa * 12600))+"\">");
    }else if(window.orientation == 0 || window.orientation == 180){
        document.write("<meta id=\"viewp1\" name=\"viewport\" content=\"width=1400px, minimum-scale=0.1,maximum-scale=2.0, initial-scale="+(window.screen.width * 4/(chengfa * 12600))+"\">");
    }else if(window.orientation == 90 || window.orientation == (-90)){
        document.write("<meta id=\"viewp1\" name=\"viewport\" content=\"width=1400px, minimum-scale=0.1,maximum-scale=2.0, initial-scale="+(window.screen.height * 4/(chengfa * 12600))+"\">");
    }
    var viewp1 = document.getElementById('viewp1');
    function changeViewp1(){
        if(window.orientation == 0 || window.orientation == 180){
            viewp1.setAttribute('content','width=1400px, minimum-scale=0.1,maximum-scale=2.0, initial-scale='+ (window.screen.width * 4/(chengfa * 12600)));
        }else if(window.orientation == 90 || window.orientation == (-90)){
            viewp1.setAttribute('content','width=1400px, minimum-scale=0.1,maximum-scale=2.0, initial-scale='+ (window.screen.height * 4/(chengfa * 12600)));
        }
    }
    changeViewp1();
    if("Safari" == mb){
        window.addEventListener("orientationchange",changeViewp1,false);
    }
    if(window.addEventListener){
        window.addEventListener("resize",changeViewp1,false);
    }else if(window.attachEvent){
        window.attachEvent("onresize",changeViewp1);
    }
}    
    </script>
</head>