sending string from processing to firmata/arduino

hej forum,
although the firmata library is extensively documented, i haven't been able to find a solution to my simple problem. so sorry, if i missed the solution somewhere / am double posting...

i am trying to send simple messages from processing to arduino, using the firmata library. i guess i could just read the serial port directly, but i like the idea of being able to use firmate for string callbacks, in stead of constantly checking and parsing the serial port in my main loop.

anyways, i can't figure out how to send a string(!) ... from http://firmata.org/wiki/Protocol#Control_Messages_Expansion i can see that sending a string needs the command 0x71 --- how is this sent?? what is the format? i would think:

serialPort.write(byte(71)+"my string here");

from processing should do the trick. but no. :-/

here is my arduino code, when sending the above nothing happens (AKA tx flashes so i receive data, but LED 13 nevers goes on, so i am never in stringCallback())

//firmata test

#include <Firmata.h>

void stringCallback(char *myString)
{
    Firmata.sendString(myString);
    digitalWrite(13,HIGH);
    delay(50);
    digitalWrite(13,LOW);
}


void sysexCallback(byte command, byte argc, byte*argv)
{
    Serial.print(START_SYSEX, BYTE);
    Serial.print(command, BYTE);
    for(byte i=0; i<argc; i++) {
        Serial.print(argv[i], BYTE);
    }
    Serial.print(END_SYSEX, BYTE);
}

void setup()
{
    pinMode(13,OUTPUT);
    Firmata.setFirmwareVersion(0, 1);
    Firmata.attach(STRING_DATA, stringCallback);
    Firmata.attach(START_SYSEX, sysexCallback);
    Firmata.begin(57600);
}

void loop()
{
    while(Firmata.available()) {
        Firmata.processInput();
    }
}

and here is my processing sketch

import processing.serial.*;
Serial serialPort;

void setup() {
  // List all the available serial ports:
  println(Serial.list());
  serialPort = new Serial(this, Serial.list()[0], 57600);
}

void draw () {
}

void mousePressed() {
  serialPort.write(byte(71)+"my string here");
}

void serialEvent (Serial myPort) {
  while (serialPort.available() > 0) {
    int inByte = serialPort.read();
    print(char(inByte));
  }
}

the sysEx callback seems to work, as i, when launching my sketch, get a return string printed in my processing output with some weird ASCII characters and then the name of my arduino sketch....

hmmm?
/j