sharp_menupopup_corners.css

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

menupopup,
.menupopup-arrowscrollbox{ border-radius: 0 !important; }
:root{ --arrowpanel-border-radius:0px !important }