userChrome.css

/* On Linux this file should be in:
      ~/.mozilla/firefox/$USER_ID.default/chrome/userChrome.css

   To be used with the awesome Tree Style Tabs addon.
*/

/* Hide horizontal tabs at the top of the window */
  @-moz-document url("chrome://browser/content/browser.xul") {
    #TabsToolbar {
      visibility: collapse !important;
      margin-bottom: 21px !important;
    }

    #sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] #sidebar-header {
      visibility: collapse !important;
    }
  }

/* Add the following code to TST's Advanced settings in the addon preferences for:
       * Compact tab layout
       * More compact layout
       * Unread tabs in read
       * Private tabs indicator

  :root { --tab-height: 20px !important; }
  .tab { height: 20px !important; }
  #tabbar[style*="margin"] { margin-top: 20px !important; }
  .tab.unread .label {
    color: red !important;
  }
  .tab.private-browsing .label:before {
    content: " ";
  }

*/