The browser test asserted CSS.supports('appearance', 'base-select') as a
precondition, so it failed in Firefox, which has no customizable select.
menu.css styles the picker only inside @supports (appearance: base-select),
and the native picker is the intended fallback there; the test now checks
that fallback where the property is missing and the M3 menu where it is.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
