firefox - userChrome.css

 /* set default namespace to XUL */
@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

#appmenu-toolbar-button {
  list-style-image: url("chrome://branding/content/icon16.png");
}

#appmenu-toolbar-button > .toolbarbutton-text,
#appmenu-toolbar-button > .toolbarbutton-menu-dropmarker {
  display: none !important;
}

.tabbrowser-tab
{
   height:             24px !important;
   min-height:         24px !important;
   max-height:         24px !important;
   font-size:          12px !important;
   -moz-border-radius:  0px !important;
   border:             none !important;
   text-shadow:        none !important;
   padding:             3px !important;
   margin-right:        3px !important;
}

.tabbrowser-tab[selected="true"]:not([pinned="true"]) {
   min-width:         36px !important;
   max-width:         36px !important;
}

.tabbrowser-tab[selected="true"] {
   font-weight:                 bold;
   background-color:  #fff !important;
   color:             #000 !important;
}

.tabbrowser-tab:not([selected="true"]) {
   color:            #C8C8C8 !important;
   background-color: #202020 !important;
   font-weight:                 lighter;
   min-width:            0px !important;
   max-width:          140px !important;
}

.tabbrowser-tab[pinned] {
   background-color: #000 !important;
   color:                       #fff;
}