nsIExternalHelperAppService Interface

 Returns true if data from a URL with this extension combination
 is to be decoded from aEncodingType prior to saving or passing
 off to helper apps, false otherwise.

boolean applyDecodingForExtension(in AUTF8String aExtension, in ACString aEncodingType)

 Binds an external helper application to a stream listener. The caller
 should pump data into the returned stream listener. When the OnStopRequest
 is issued, the stream listener implementation will launch the helper app
 with this data.
 @param aMimeContentType The content type of the incoming data
 @param aRequest The request corresponding to the incoming data
 @param aWindowContext Use GetInterface to retrieve properties like the
                       dom window or parent window...
                       The service might need this in order to bring up dialogs.
 @return A nsIStreamListener which the caller should pump the data into.

nsIStreamListener doContent(in ACString aMimeContentType, in nsIRequest aRequest, in nsIInterfaceRequestor aWindowContext)