mobile-config-firefox/chrome/menubar_in_main_toolbar.css

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

/* Make menubar permanently enabled or this isn't going to work */

#navigator-toolbox{ --uc-menubar-height: 34px; }
:root[uidensity="compact"] #navigator-toolbox{ --uc-menubar-height: 30px }

#titlebar{
  -moz-box-direction: reverse; /* Fx <112 compatibility */
  flex-direction: column-reverse;
  -moz-appearance: none !important;
}

#toolbar-menubar{
  margin-bottom: calc(0px - var(--uc-menubar-height));
  height: var(--uc-menubar-height);
  position: relative;
  z-index: 2;
  pointer-events: none;
}

#menubar-items{
  -moz-box-pack: center; /* Fx <112 compatibility */
  justify-content: center;
  pointer-events: initial;
  margin-top: 3px;
  color: var(--toolbar-color);
}
/* Adjust to fit menubar items - 300px works for English locale */
#nav-bar{ padding-left: 300px; }

#toolbar-menubar > .titlebar-buttonbox-container{ display: none }
:root[tabsintitlebar][sizemode="normal"] .titlebar-spacer,
:root[tabsintitlebar] #TabsToolbar > .titlebar-buttonbox-container{ display: flex !important; }