Entitlement and true idiocy. It was so entertaining to read because the author is moaning and bitching about using an experimental feature. Great candidate for being an IE6 advocate.
The developers are pretty unsympathetic though. That disclaimer on the third paragraph of CSS_Reference/Mozilla_Extensions? It might as well have been on display in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying 'Beware of the Leopard'. I understand the reasoning for removing the prefixed version, but they should at least give the developers more warning!