Thanks for the advice Paul. I just tried ServoFirmata and the ESC worked fine.
Perhaps I should have clarified, but I've got several more actuators and sensors connected to the Mega that need to communicate with the computer, so ServoFirmata alone won't work. I know StandardFirmata supports servos since I can run the ESC from Firmata Test with StandardFirmata on the Arduino and all the sensors, etc. running, but for some reason I can't control servos from Processing.
So what I'd just love to know is if the Processing library is buggy or if I'm just using it wrong.
Here's my Processing test code (which incidentally controls the motor with a joystick rather than a mouse or arrow keys.) It works fine when Servo
Firmata is running on the Mega.
int escPin = 3;
controll = ControllIO.getInstance(this);
device = controll.getDevice("Generic USB Joystick ");
xSlider = device.getSlider(0);
arduino = new Arduino(this, Arduino.list(), 57600);
xVal = xSlider.getValue();