@ajfisher, the rwaldron/johnny-five#665 thread seems to be stalled at the moment. Meanwhile I was wondering if I can use firmata's I2C operations to control the mBot's Led Matrix module.
The MakeBlocks official wiki page of the Led Matrix module indicates that it's controlled via the I2C interface: http://learn.makeblock.com/en/me-led-matrix-8x16/ : "The Me LED Matrix contain 128 pieces of matrix LED.There are 8 piece per line and 16 per row. The main board sends the data to module through I2C bus, and LED control specific chip in module can handle the data and interpret it. And output relative signal to power on or off the LED. Make them display the content."