@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

tab,
.tabs-alltabs-button,
.tabbrowser-arrowscrollbox > .scrollbutton-up,
.tabbrowser-arrowscrollbox > .scrollbutton-down
{
border: 0 !important;
background: transparent !important;
height: 21px !important;
}