fenix-fox/chrome/hide_tabs_toolbar.css

/* Hide tabs toolbar Fx65+ */
:root{
  --uc-toolbar-height: 32px;
  --uc-window-control-width: 138px;
}
#navigator-toolbox{ --window-drag-space-width: 24px; }

:root:not([uidensity="compact"]){--uc-toolbar-height: 38px}


#TabsToolbar{visibility: collapse}

:root:not([inFullscreen]) #nav-bar{
  margin-top: calc(0px - var(--uc-toolbar-height));
}

/* Space to drag the window on both sides of navbar */
:root[tabsintitlebar="true"]:not([inFullscreen]) #nav-bar{
  padding-right: calc(var(--uc-window-control-width) + var(--window-drag-space-width,0px));
  padding-left: var(--window-drag-space-width,0px)
}

#toolbar-menubar{
  min-height:unset !important;
  height:var(--uc-toolbar-height) !important;
  position: relative;
}

#main-menubar{
  -moz-box-flex: 1;
  background: var(--toolbar-non-lwt-bgcolor);
  background-clip: padding-box;
  border-right: 30px solid transparent;
  border-image: linear-gradient(to left, transparent, var(--toolbar-non-lwt-bgcolor) 30px) 20 / 30px
}

#toolbar-menubar:not([inactive]){ z-index: 2 }
#toolbar-menubar[inactive] > #menubar-items { opacity: 0 }