I don't know Mageia or FreeBox but I just logged onto a 320 from a PC running Fedora 14 and FireFox (ver 3 I think).
I noticed that FireFox has an annoying habit of immediately converting
http://Nas-Office
to
http://www.Nas-Office.com
and then giving me a 404 error. To connect to the NAS I had to first connect to the router (I know its IP address) and check the DHCP leases to find the IP address of the NAS. Once I entered the IP address of the NAS into FireFox I was presented with the usual login screen and was able to do all the normal things.
I don't know if that helps or not but it is all I have to offer I'm afraid.
Jack