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

/* Legacy code: New Tab Button Position (for those that have the extension */
#tabs-newtab-button-start,
#tabs-newtab-button-end,
#tabs-newtab-button-left,

/* Default buttons: Add your own when applicable */
.tabs-newtab-button,
.tabs-alltabs-button,
.scrollbutton-up,
.scrollbutton-down
#tabview-button

/* This is the width: Change to your desired preference. */
{
width: 40px !important;
}