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.
Resumen
:-moz-handler-disabled selecciona elementos que no pueden ser mostrados porque sus manejadores han sido deshabilitados por el usuario.
Es útil principalmente para desarrolladores de temas.