.roundcorner{
border-radius:6px; /*css3 - but not supported yet*/
-webkit-border-radius: 6px; /*mozila - firefox, iceweasel */
-moz-border-radius: 6px; /*webkit - google crome, midori, safari */
}

and more

-moz-border-radius-topleft / -webkit-border-top-left-radius