You will need a USB-485 adapter. I personally prefer adapters from either B&B Electronics or NI. There are many other manufactures as well.
DB-9 connection at you MFC includes two groups of signals. Pins 3 and 4 supply power to the MFC. Pins 6-9 are signals associated with the 485 interface. You will need to build a custom cable that connects the MFC, DC supply and the USB-485 converter together.