If you mount it (say, by a Device Manager), then FIleZilla Client will see it where it is mounted (see the attached screenshot).
I have done many a transfer like that.
Look:
On the left is my laptop and on the right is Red Eagle STB with an external HDD mounted as HDD and you can easily transfer stuff to and fro...
In my "A pretty thorough PBNIGMA II VX guide for Ferrari 500 HD by gorski_12.12.12" - on page 29 you have info as to how to work with FZC. Transfers are easy and they work, if they are not very fast...
You also have detailed info how to mount a device and so on...
If you really are worse than me maybe this can help...
Yeee.... Transfer in configuration HD(ext4)-eSATA->STB(xtrend)-10GbLAN->PC(win7) is about 30-35MB/s. Direct connection via eSATA - over 70MB/s.