How to select which network adapter Firefox should use for specific sites

Question

I have a PC with different network adapters that provides different internet connections.

How can I setup Firefox (or another browser) to access certain site using one network adapter and other site using another adapter?

Or more in general, how can I force a software application to use a network connection and another software to use another connection?

My OS is Windows XP.

Solution

In general, it is the operating system, not the application, that decides which network adapter to use, based on target IP-addresses.

If you can arrange that the different adapters are on different subnets, you can set up static routes for the IP-addresses of the websites.

I guess most PCs have their IP-addresses allocated by the local router. These can be configured so that a multi-homed PC gets different subnets for different interfaces.

   ISP1........Router1----------PC----------Router2........ISP2
                       subnet1     subnet2

Comments

[Gilles 'SO- stop being evil']

Doing exactly what you ask is probably not possible. But it may be possible to fulfill your underlying requirement in a different way (perhaps using a proxy or changing your routing configuration). So what are you trying to do? You may also be interested in a somewhat similar question on Linux: bind software to different network interfaces, 2 network interfaces connected to internet. Choose the one to use according to the domain name.