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.
Some time has passed. In the current firefox version you can check "Remote DNS" directly in the Network settings where you set the proxy settings.
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.