systemwise proxy server?

I just found that proxy server setting in system pref-network is not systemwise. That is, that setting is applied to safari only. If I want to use proxy server in firefox, I have to set it up again. Thus, I am wondering that is there any systemwise proxy server setting?

 

Thanks for the reply.
I should be more clear about what I intend to do. For instance, in linux, I can use iptable to redirect my packet traffics, which go to destination port 80, to some addresses.

I can forward my packets to address:10.0.0.1 using following command:
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to-destination 10.0.0.1:80


Therefore, I want to implement such policy and enforce every packet with destination port 80 to use a designated proxy server. How can I achieve this?

 

After digesting the manual, I come up with the following command.

ipfw add 1000 fwd my_proxy_address,3128 tcp from any to any 80

I can observe my packets went through my proxy server. But, this command will crash the system whenever I test some flash games on facebook. Did I do anything wrong in this command?

However, if I setup the proxy server manually in the system pref, I wouldn't encounter any crash at all, which indicates my proxy server functions properly. This is quite strange to me since ipfw should forward every raw packet to my proxy server.

So, what's wrong behind all this? I'll appreciate it much if you can either help me fix ipfw or provide a better solution.