gecko/browser/base/content/tabbrowser.css

.tabbrowser-tabbox {
  -moz-binding: url("chrome://browser/content/tabbrowser.xml#tabbrowser-tabbox");
}

.tabbrowser-arrowscrollbox {
  -moz-binding: url("chrome://browser/content/tabbrowser.xml#tabbrowser-arrowscrollbox");
}

.tab-close-button {
  -moz-binding: url("chrome://browser/content/tabbrowser.xml#tabbrowser-close-tab-button");
  display: none;
}

.tabbrowser-tabs:not([closebuttons="noclose"]):not([closebuttons="closeatend"]) > .tabbrowser-tab[selected="true"]:not([pinned]) > .tab-close-button,
.tabbrowser-tabs[closebuttons="alltabs"] > .tabbrowser-tab:not([pinned]) > .tab-close-button {
  display: -moz-box;
}

tabpanels {
  background-color: white;
}

.tab-drop-indicator {
  position: relative;
  z-index: 1;
}