OEL5.4 OS, eth0 has private IP, eth0:0 has routable IP, internet access don't work

[Hiroshi]

I have a OEL5.4 server with a eth0 set up with private IP (non-routable), I've added eth0:0 with a routable IP address.

I've used:
# ifconfig eth0:0 routable-IP netmask ----- broadcast ------
and
# route add default gw gw-IP-address eth0:0

commands to set up eth0:0.

How do I tell firefox to use eth0:0 to be able to access the internet?

Any help would be highly appreciated; many thanks in advance.