Oops, didn’t read the OP well enough.
USB itself is not made for networking (USB to USB). The origin of USB was replacing serial and parallel cables, but not networking, since it is a point-to-point connection with different behavior on both sides (host vs. device).
What I meant was using a USB to Ethernet adapter. That might work if the driver is already in the system, but probably only the driver for the internal ethernet interface chip might be present, so you probably need an USB to Ethernet Interface with the same chip (family) if it works at all.
That doesn’t make sense in almost all cases since there already is an ethernet port present at the FMB.
But if there is a port forwarding to an IP address that is identified with the MAC-address of the USB-to-Ethernet adapter present in the router AND you want to use an FMB and a Windows or Linux machine alternatively, then it makes sense.
But this is the only option that makes sense to me and if you do not understand this, then you don’t need it or meant an USB-to-USB-connection which is not possible and doesn’t make sense to me anyway.