Configuring a browser to only use the second network adapter

I have a dell laptop running WINXPpro that I use on my corporate network, connected via the built-in 10/100/1000 NIC. For corporate use, I utilize the IE6 browser. The corporate network has a proxy that prevents access to some external URL’s, how ever I have a legitimate need to get to those sites. I am trying to find out how I can configure my other web browser (Firefox) to only route out of my Cellular PC card while still connected to the corporate network. Essentially, it is a multihomed machine, and I need to keep all my apps functioning on the NIC for corporate use, while being able to use my second browser only through my cellular PC card. Is this possible?