The WWW object, when running in the Unity Editor, passes a wide-open Accept header (value /) and does not include the Accept-Encoding header.

The HTTP specification states that failing to include an Accept-Encoding header indicates that the client can accept all encodings.

As a result, the crossdomain.xml file is sent to Unity gzipped/compressed, which our WWWCurl object cannot handle. It treats the data as garbage and throws an error indicating that Unity could not retrieve the crossdomain.xml file.

This prevents all WWW requests from working on web servers that serve compressed/gzipped content; this is most high-volume websites out there today.

This is a problem for all platforms that use curl (Unity editor, standalone platforms).