ESP8266 firmware update using espruino pico

which seems to be expected with this old firmware. Correct?

Yes... So that sounds like everything is connected right.

I've just tried this here and it works for me with 1v80. However, if I didn't reset the ESP8266 right (with GPIO0+RST) I get exactly the error you described.

• Did you disconnect the Web IDE after writing the code
  
• When you run the esptool command, does the blue LED on the ESP8266 flash at all?