How to secure Firefox traffic (+DNS) through SOCKS proxy under Ubuntu 10.04?

Firefox has an about:config setting that controls whether or not DNS gets routed through your proxy. It's off by default. I forget the setting name, but if you use the filter, it should not be hard to find.

You can verify that all your traffic is going through the SSH proxy by viewing the packets coming from your computer. This can be done by putting your NIC or wireless card into Permiscuous Mode and using a program like TCPDump or Wireshark(I recommend wireshark).

Using these programs you can see the network traffic and filter for a specific protocol of packets such as DNS. If you filter for DNS while the proxy is on and receive any packets (labeled as DNS) then at least some DNS requests aren't going through the proxy. The reason for this is because if they are going through SSH the only traffic you will see will be SSH.

There's a few things you need to watch out for, some plugins such may access the internet without using the proxy setting and can leak information. Firefox has a host of great addons which help make sure that everything goes through the proxy, check those out.

Good luck!