ff火狐中不响应js的onclick事件

我做了一个显示隐藏功能菜单的效果，在ie下能正常使用，而在FF下没有响应，更改了些js也没有反应，网上也找不到相应答案。请那位高手来解决一下。代码如下：html<html><body><div class="bleft" id="main_Left" style="display:block;"></div> <div class="bright" id="main_right" style=""> <div class="bright_l" id="main_right_left"> <div class="hidden" id="on_off" onclick="hid_off();">点击隐藏左侧</div></div></body></html>css:.bright{ width:820px;position:absolute;right:16px;top:-7px; height:auto;background:url(../images/right_bg_top1.gif) no-repeat;}/*宽屏显示*/.bright2{ width:971px;position:absolute;right:16px;top:-7px; height:auto;background:url(../images/right_bg_top.gif) no-repeat;}.bright_l{padding-left:26px;background:url(../images/right_bg_l_05.gif) no-repeat;position:relative;}.bright_l2{padding-left:26px;background:url(../images/right_bg_l_06.gif) no-repeat;position:relative;}/*宽屏显示*/.hidden{ display:block; background:#d6d6d6; padding:1px; width:14px; position:absolute; left:7px; _left:-19px; top:284px; color:#333; text-align:center; cursor:pointer;} js:<script language="javascript" type="text/javascript"> var $=function(id){return document.getElementById(id);} function hid_off(){ var txt_b=$("on_off").childNodes[0]; if(txt_b.innerHTML=="点击隐藏左侧"){ $("main_left").style.display="none"; $("main_right").className="bright2"; $("main_right_left").className="bright_l2"; $("on_off").innerHTML=" 点击显示左侧"; } else{ $("main_left").style.display="block"; $("main_right").className="bright"; $("main_right_left").className="bright_l"; $("on_off").innerHTML="点击隐藏左侧"; } } </script>

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