==================
OK.  It gets very complex after this...  But you have two options... 
One is IPsec tunneling over the internet.  Slow, but secure.  The other is
to create a link on the INTERNAL side of the firewall.  This is adding a nic
to firewall A with an IP in the subnet of firewall B and adding static
routes to both firewalls.  The method used to do this can be a long cable, a
leased line, or wireless.  This will be much faster, and also secure.

			Lee
==================

Hi Lee, the IP Tunneling is out of the question since I need performance.
Security is no issue. When you said adding NIC to firewall A, do you mean
the Firewall A have 3 NICs? Would this be the correct picture you mentioned?
The wireless antenna only works as a bridge.

Would the settings below works to make both company communicates as if they
are in the same location? If not please tell me what would work. So far, I
am able to make all devices behind Firewall B to contact all devices behind
Firewall A (including internet) successfully and no problems at all, but not
the other way around. Any devices behind firewall A cannot access any
devices behing Firewall B

(PS: all firewalls are running m0n0wall)
Firewall A:
Nic 1: WAN 118.x.x.x / 29
Nic 2: LAN 192.168.0.5 / 16
Nic 3: Bridge to FW A??? 10.0.0.2 / 24
Add Static Route for 192.169.x.x to point to gateway 192.169.0.5???

Firewall B 
Nic 1: WAN 10.0.0.50 / 24 --> Treat this as bridge?
Nic 2: LAN 192.169.0.5 / 16
Add Static Route for 192.168.x.x to point to gateway 192.168.0.5???
Then set all the users in company B with 192.169.x.x /16 with gateway and
dns to 192.168.0.5? For Internet sharing.