I think Yucandu has (custom) hardware (like something based on an esp32 circuit board) that he wants to flash with new firmware, and you generally do that via a com-port (remnant of an old type of connector). Oversimplified: These days com-ports are simulated over usb, and (for now) only chrome-based browsers can actually send the firware over these simulated ports. An example is the flasher for Meshcore devices.