ie6和ie7

#tip {
*background:black; /*IE7 背景变黑色*/
_background:orange; /*IE6 背景变橘色*/
}

IE8和IE9

:root .test { color:#963\9; } /* IE9 only */  

firefox
@-moz-document url-prefix(){.bt_comment_ico{top:-1px;}}

ie系列
*html .ico_tj{background:none;filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(enabled=true,sizingMethod=scale,src=http://www.mamicode.com/‘http://#‘);}
FILTER: progid:DXImageTransform.Microsoft.gradient(GradientType:1, startColorstr=#70000000,endColorstr=#70000000);
filter:alpha(opacity=80);
opacity:0.8;