:root[sizemode="normal"]{ border-top: none !important }
#navigator-toolbox::after{ content: none !important }

/* Removes few remaining extra lines above tabs in non-maximized windows */
/* Also prevents small vertical shift when moving tabs in compact density - who knows why */
:root[sizemode="normal"] #titlebar{ -moz-appearance: none !important; }


/* OPTIONAL - uncomment to remove still remaining space atop of tabs */
/* This just increases the height of tabs by few pixels, not decrease the toolbar height */

/* Fx pre-65 */
/* #navigator-toolbox > #TabsToolbar{margin-top: -2px;} */
/* Fx65+ */
/* #TabsToolbar > .toolbar-items > spacer{ display: none; } */