SSH Tunnel as Proxy – No Data Returned Issue

I'm trying to set up an SSH tunnel as a web proxy for use when I'm at public locations. I already have a remote server to use, and I've also had this working in the past using this same server. However now when I try it, I successfully make the SSH connection, but the webbrowser returns no data for each page I visit.

The SSH command I'm using is:

ssh -ND 8080 -p 20000 myusername@myserver.com

This connects properly. If I don't include the -N, then I correctly see a remote shell, so the connection is successful.

However, when I set my browser to use the local proxy – each page returns no HTML data. It also doesn't return any errors. Literally just a blank page. Note that if I disconnect the SSH connection – then the browser shows a proxy error. So the browser is definitely doing something with the proxy.

If I try this is Chrome, then I get a chrome error explicitly saying "no data returned". If I try this in Firefox, then I just get a blank page.

Note that I'm only trying this from one public location. I'm on holiday at the moment, and am using the apartment's wifi connection. So I guess it's possible that it's something to do with their setup. However, given that I can successfully SSH to my server – I'm not sure what in their configuration could make a difference. Note that I've also tried including the DNS lookups through the proxy.