Patch release: 3.3.1 fixed the colour mismatch between arrow panels and context menus, but the shape mismatch was still there.
Fixed
Popup corners are square again. Toolkit's popup.css defaults --panel-border-radius to 6px for arrow panels (hamburger menu, extensions popup, shield/permissions popup), while context menus sit at 0 via their own code path – so panels stood out with rounded corners against FoxOne's otherwise square chrome (findbar, context menus, breakout urlbar). Both now pin to 0.