Underline for sorted Grid headers in Mozilla

Hi,

I am not getting underline for sorted grids in mozilla but is worlking in IE.

Code is :
this.getHeaderTemplate().setClass("head","under");[or]
this.getHeadersTemplate().setClass("head","under");
CSS is :

.aw-head-under{
text-decoration:underline;
}

Could you please help me?

Regarrds,
Srini.