                        課程
                    
                        /前端開發(fā)
                        
                            /JavaScript
                        
                        /Tab選項卡切換效果

求大神指導，在火狐里有BUG

<!DOCTYPE?html>
<html>
????<head>
????????<meta?charset="UTF-8">
????????<title>發(fā)送驗證碼練習</title>
????<style?type="text/css">
????????.nosend{width:?120px;height:?50px;background-color:?#999999;color:?#FFFFFF;margin:?30px?400px;}
????????.send{width:?120px;height:?50px;background-color:?#0C4E7C;color:?#FFFFFF;margin:?30px?400px;}
????</style>
????</head>
????<body>
????????<input?type="button"?id="send"?value="發(fā)送驗證碼"?class="send"/>
????</body>
????<script?type="text/javascript">

????????var?mybtn=document.getElementById("send");
????????var?timer=null;
????????var?index=10;
????????mybtn.onclick=function(){
????????????if(timer){clearInterval(timer);timer=null;}
????????????mybtn.setAttribute("disabled","disabled");
????????????mybtn.setAttribute("class","nosend");
????????????timer=setInterval(function(){
?????????????index--;
?????????????mybtn.value=index+"后重新發(fā)送";
?????????????if(index<0){
?????????????????clearInterval(timer);
?????????????????mybtn.removeAttribute("disabled");
?????????????????mybtn.setAttribute("class","send");
?????????????????mybtn.value="重新發(fā)送驗證碼";
?????????????????index=10;
?????????????}
????????????},1000);
????????}

????</script>
</html>

這是完整代碼，有一個BUG，在火狐瀏覽器里第一次運行正常，當刷新頁面的時候會自動加上一個disabled屬性，而在谷歌瀏覽器里就正常，這是為什么呢？

還有，提示里的disabled屬性設置為‘true’或‘false’好像并不管用。