I am using Firefox 3.5.7 with FoxyProxy. I have an ssh tunnel forwarding 8080 through to an HTTP proxy server on the other end. With FoxyProxy, I send work traffic direct but everything else goes through the proxy server. DNS lookups, though, still go to work's DNS servers for resolution. Is there an add-on that can funnel certain DNS traffic to the OS but shove everything else through my ssh tunnel? It's a long shot, but it never hurts to ask....
In firefox type this in your address bar:
Click that you promise to be careful.
In the filter textbox, type: proxy
Find the preference name called network.proxy.socks_remote_dns. Double click it to set it to true.
Firefox will now proxy DNS requests instead of trying to resolve them locally.
Configure your ssh client to do Dynamic forwarding (-D flag on the openssh client) so that it acts like a SOCKS server. Then you can do remote DNS lookups via SOCKS. A straight up HTTP proxy doesn't support what you want.
FoxyProxy has info on how to do what you want with SOCKS. Privoxy is another good option, too.