Since this subject comes up often I am writing a definitive statement.
Fireworks (layered) PNG files
There is no such thing as "layered PNG". The PNG standard does not define a way to store layers, and only deals with flattened images.
Fireworks saves out additional layer data to PNG files in a proprietary format using a private tag. A definition for this proprietary data has never been made public. A PNG saved by Fireworks can still be used as a flattened image by any applicati