I keep investigating and I just noticed something.
Using USB uart, the firmata firmware on the Uno waits for DTR to send its initialization string (the version + blahblah).
Using the RFBee link the initialization string is not sent so the communication doest not start.
Maybe you could or someone tell me if the DTR signal is used by the RFBee?
If the PC changes the DTR, does RFBee transmit the value to the other to set the value of the arduino uart?
I’m afraid only data are transmitted and no signal like DTR 