userChrome.css

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


/* hide the native tabs */
#main-window:not([privatebrowsingmode]) #TabsToolbar {
  visibility: collapse;
}


/* hide the sidebar header */
#sidebar-header {
  display: none;
}


/* hide the sidebar in fullscreen mode */
#main-window[inFullscreen] #sidebar-splitter, #main-window[inFullscreen] #sidebar-box {
  display: none;
}


/* shrink the sidebar splitter to 1px */
#sidebar-splitter {
  width: 1px !important;
  border-style: none !important;
  background-color: unset !important;
}