userChrome.css

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

:root {
  /* fix for full screen mode */
  --tab-toolbar-navbar-overlap: 0px !important;
  /* set minimum tab height  */
  --tab-min-height: 24px !important;
}

#TabsToolbar {height:var(--tab-min-height)!important; margin-top:-1px!important; margin-bottom:1px!important}
/* Override vertical shifts when moving a tab */
#TabsToolbar[movingtab] {padding-bottom:0px!important}
#TabsToolbar[movingtab] > .tabbrowser-tabs {padding-bottom:0px!important; margin-bottom:0px!important}
#TabsToolbar[movingtab] + #nav-bar {margin-top:0px!important}


/*
 * Make the toolbar extra-compact (similar to v56 with CTR)
 *
 * Applies to Compact density
 *
 * Contributor(s): Alex Vallat
 */

:root[uidensity=compact] #urlbar,
:root[uidensity=compact] .searchbar-textbox {
  font-size: unset !important;
  min-height: 18px !important;
}

:root[uidensity=compact] #identity-box {
  max-height: 20px;
}

:root[uidensity=compact] #nav-bar .toolbarbutton-1 {
  padding: 0px !important;
}

/* Compatibility with auto-hide.css */
:root[uidensity=compact] #navigator-toolbox {
  --nav-bar-height: 24px !important;
}