fenix-fox/chrome/autohide_main_toolbar.css

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

/* This style hides the main toolbar and shows it when the cursor is over the tabs toolbar as well as whenever the focus is inside nav-bar, such as when urlbar is focused. */

:root{ --uc-navbar-transform: -40px }
:root[uidensity="compact"]{ --uc-navbar-transform: -34px }

#navigator-toolbox > div{ display: contents; }
:root[sessionrestored] :where(#nav-bar,#PersonalToolbar,#tab-notification-deck,.global-notificationbox){
  transform: translateY(var(--uc-navbar-transform))
}
:root:is([customizing],[chromehidden*="toolbar"]) :where(#nav-bar,#PersonalToolbar,#tab-notification-deck,.global-notificationbox){
  transform: none !important;
  opacity: 1 !important;
}

#nav-bar:not([customizing]){
  opacity: 0;
  transition:  transform 400ms ease 1.8s, opacity 400ms ease 1.8s !important;
  position: relative;
  z-index: 2;
}
#TabsToolbar{ position: relative; z-index: 3 }

/* Show when toolbox is focused, like when urlbar has received focus */
#navigator-toolbox:focus-within > .browser-toolbar{
  transform: translateY(0);
  opacity: 1;
  transition-duration: 500ms, 200ms !important;
  transition-delay: 0s !important;
}
/* Show when toolbox is hovered */
#titlebar:hover ~ .browser-toolbar,
#nav-bar:hover,
#nav-bar:hover + #PersonalToolbar{
  transform: translateY(0);
  opacity: 1;
  transition-duration: 500ms, 200ms !important;
  transition-delay: 0s !important;
}

/* Bookmarks toolbar needs so extra rules */
#PersonalToolbar{ transition: transform 400ms ease 1.8s !important; position: relative; z-index: 1 }

/* Move up the content view */
:root[sessionrestored]:not([inFullscreen]) > body > #browser{ margin-top: var(--uc-navbar-transform); }