I have established an SSH tunnel to an untrusted machine:
ssh -N -D 12345 firstname.lastname@example.org
Next, I set up Firefox's connection settings to use the SSH tunnel by setting the SOCKS host to 127.0.0.1, and the SOCKS port to 12345.
I do not need to hide the fact that I am proxying http requests, but I am concerned that this setup allows the untrusted machine to eavesdrop on the contents of the traffic when I browse the web. Is this a valid concern?