nsIUnicharStreamListener is very similar to nsIStreamListener with
 the difference being that this interface gives notifications about
 data being available after the raw data has been converted to
 UTF-16.

 nsIUnicharStreamListener

 @status FROZEN
[scriptable, uuid(4a7e9b62-fef8-400d-9865-d6820f630b4c)]
interface nsIUnicharStreamListener : nsIRequestObserver

Methods

 Called when the next chunk of data (corresponding to the
 request) is available.

 @param aRequest request corresponding to the source of the data
 @param aContext user defined context
 @param aData the data chunk

 An exception thrown from onUnicharDataAvailable has the
 side-effect of causing the request to be canceled.
void onUnicharDataAvailable(in nsIRequest aRequest, in nsISupports aContext, in AString aData)