(BTW...the adapter is ok. Tested with Windows...)
This means literally less than nothing. Because m0n0wall, FreeBSD, Linux, and Mac are not Windows. For that matter Windows isn't always Windows. (Look how much hardware has no Win7 64bit drivers?)
And USB nics have issues in FreeBSD anyway. (As do USB drives) Is there anything else you can use? Is there another USB nic you can try? What is the actual chipset in the nic? (If unknown, you will need to boot linux or FreeBSD full and type lspci or pciconf -lv to fin out.)