Comment # 6 on bug 1160331 from Fabian Vogt

Instead of

                mFileURL = nsCString( "file://" );
                mFileURL.Append( output[ 0 ] );

it should look like this (untested):

                nsCOMPtr<nsIFile> localfile;
                nsresult rv = NS_NewNativeLocalFile( output[ 0 ],
                                      PR_FALSE,
                                      getter_AddRefs(localfile));
                if (NS_FAILED(rv))
                    return v;

                rv = net_GetURLSpecFromActualFile(localfile, mFileURL);
                if (NS_FAILED(rv))
                    return v;