Have you taken a look at the default css generated by the plugin on its admin page? Specifically:
/* Default CSS generated by dTabs */
/* style the tabs in IE (the trailing comma prevents other browsers from reading this) */
.tabbar li, .tabbar ul li, {
/* make them horizontal in IE*/
display: inline;
/* space them a little in IE*/
margin: 0 5px;
}
/* style the tabs */
.tab, .tabselected {
/* make them horizontal in Firefox 2*/
display: -moz-inline-box;
/* make them horizontal in all other browsers*/
display: inline-block;
}
Hope that helps 😉