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-crashed selecciona elementos que no pueden ser mostrados porque el plugin para dibujarlos ha dejado de funcionar.
Es útil principalmente para los desarrolladores de temas.