No estándar
This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.


La   pseudo-class CSS :-moz-system-metric(images-in-menus) selecciona un elemento si el interfaz de usuario del equipo soporta imágenes en menús.

Está pensado sobre todo para desarrolladores de temas.