mobile-config-firefox/chrome/autohide_menubar.css

/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/autohide_menubar.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */

/* Makes menubar behave like on mac */
/* Menubar will be shown when cursor touches top of the spacers on both side of tabs. Window controls will be in menubar, so they are automatically hidden */
/* Make sure you have menubar enabled */

#TabsToolbar > .toolbar-items{ position: relative; z-index: 5; }
#toolbar-menubar > .titlebar-buttonbox-container{ float: right; display: block }
#TabsToolbar > .titlebar-spacer{ display: -moz-box !important; }

#toolbar-menubar{
  --uc-menubar-height: 36px;
  position: fixed;
  display: block;
  width: 100vw; 
  height: var(--uc-menubar-height);
  margin-top: calc(8px - var(--uc-menubar-height));
  transition: margin-top 150ms linear !important;
  -moz-window-dragging: no-drag;
  z-index:4;
}

#menubar-items{ display: block; float: left; }

#toolbar-menubar:hover{
  background-color: var(--toolbar-bgcolor) !important;
  margin-top: 0px;
  z-index: 6
}