fenix-fox/chrome/menubar_in_tabs_toolbar.css

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

:root:not([customizing]) #titlebar{
  -moz-box-orient: horizontal; /* Fx <112 compatibility */
  flex-direction: row;
}
#toolbar-menubar > .titlebar-buttonbox-container,
#toolbar-menubar > spacer{ display: none; }

#main-menubar{
  -moz-box-flex: 1; /* Fx <112 compatibility */
  flex-grow: 1 !important;
}
:root:not([customizing]) #toolbar-menubar[autohide][inactive]{ max-width: 0 }

#TabsToolbar > .titlebar-buttonbox-container{
  display: flex !important;
  visibility: visible !important;
}