If on Linux/OSX, SSH to some machine with the -D option, which makes a **D**ynamic SOCKS5 proxy.

  $ ssh -D 1080 some.machine.com

This makes port 1080 on your local machine a tunneling proxy.  If on Windows, you can do this with [[http://www.chiark.greenend.org.uk/~sgtatham/putty/|PuTTY]], see [[http://thinkhole.org/wp/2006/05/10/howto-secure-firefox-and-im-with-putty/|this page]] for details.

Either way, set Firefox to use your tunnel:

First, go to options | Advanced | Network tab | Connection settings:

{{:ff-proxy1.png|}}

Then in the proxy dialog, select to "Manual" and blank out everything but "SOCKS Host", which is set to "127.0.0.1:1080":

{{:ff-proxy2.png|}}

You should be able to surf through the tunnel now.  Check http://whatismyipaddress.com/ and verify that the IP shown is the one from the machine you connected to via SSH.

If you tend to do this a lot, consider installing the SwitchProxy extension for Firefox, which will let you change proxies in two clicks:

{{:ff-proxy3.png|}}