Firmware Update

I've just taken delivery of a pre-order Espruino. I think it has 1.43 firmware on it.
I have Chrome 33. Win 8.1 Pro

I can connect in web IDE. It says 'upgrade firmware'. I can see firmware URL
in the upgrade page as soon as I go to it: http://www.espruino.com/binaries/espruino_1v53_espruino_1r3.bin

I follow the instructions

• Disconnect then connect - check URL appears. All fine.
  
• Disconnect, then press BTN1 and then RST - I get nice blue glowing LED
  
• But now... Windows beeps to say device disconnected, the list of serial ports
  is empty..
  
• Connect says "invalid serial port"
  
  

I can't get beyond this. It seems that as soon as I'm in firmware update mode, the
serial port isn't there. Strangely, the port IS present in control panel / devices

I have Win 8.1, and I've installed the CDC driver.

Any ideas? I suspect my firmware is so old I must use another method?