Fist open ssh-connection with -D, like:
ssh -D 1234 firstname.lastname@example.org
Then in Firefox, in Edit / Preferences / Advanced / Network / Settings, choose Manual proxy configuration, the Use this proxy server for all protocols has to be unchecked, in SOCKS Host put localhost and in Port 1234. Make sure that all the other lines are empty (well it’s ok if there is 0 on other Port lines).
Now you can browse as if you were browsing from some.host.somewhere. This is handy if the people at host.somewhere do not provide a real proxy server.
(That 1234 above can be any number between 1024–49151.)