I installed Oracle VirtualBox v4.3.36 and only ticked "NAT Networks" which is default mode from:
File Menu -> Preferences -> Network
then installed FreeBSD on it and it can connected to internet without any problem, altough it has some limitation which of cource these limitations normally don't affect normal network use:
Thanks to SUN Microsystems and Oracle Corporation.
---------- Post updated at 06:53 AM ---------- Previous update was at 03:51 AM ----------
I changed "DNS nameserver" on FreeBSD from:
#bsdconfig
-> Networking Management -> DNS nameservers
and changed it from 127.0.0.1 to 10.0.2.3
problem solved! on VirtualBox I did not have to deal with this problem. I think this problem was created by me, because several times when my modem was turned off I configured ethernet interface on FreeBSD with enabling and disabling DHCP, I'm not sure, just likely.