userChrome.css

#sidebar-box[sidebarcommand^="containertabs"] #sidebar-header {
  display: none;
}

#navigator-toolbox {
  /* put titlebar and url bar next to each other */
  display: -webkit-box !important;
  /* more places to allow dragging */
  -moz-window-dragging: drag;
}

#urlbar-container {
  /* more drag handles */
  -moz-window-dragging: drag;
}

#urlbar {
  /* but don't interfere with selecting text in the URL bar itself */
  -moz-window-dragging: no-drag;
}

#TabsToolbar {
  min-width: 90px;

  /* blend with macos titlebar color */
  background-color: transparent !important;
}

/* to hide the native tabs */
#TabsToolbar .toolbar-items {
  visibility: collapse;
}

#nav-bar {
  /* flat style, to blend with native window */
  background-color: transparent !important;
  box-shadow: none !important;
  /* let it breathe */
  margin: 5px 0 !important;
  /* allow dragging from the padding around the nav bar */
  -moz-window-dragging: drag;
  /* expand to fill space not taken by #TabsToolbar */
  -moz-box-flex: 1000;
}

/* contains private browsing badge and fullscreen button */
#titlebar-secondary-buttonbox {
  margin-left: 4px;
}

.titlebar-spacer[type="pre-tabs"] {
  display: none !important;
  border-inline-end: none !important;
}

/* put a top-border on the main content rather than a bottom-border
   on the toolbar, because the toolbar has -moz-appearance: none; */
#content-deck {
  border-top: 1px solid #cccccc;
}