The answer was, as very often, extremely simple and silly. In the 'Connection Settings' tab in Firefox I had set 'Manual Proxy Configuration' and I had put 127.0.0.1 as the IP and 1080 as the port number for all three of 'HTTP Proxy', 'HTTPS Proxy' and 'Socks Proxy'. For some reason this no longer works (it certainly used to). I have cleared out the HTTP Proxy and HTTPS Proxy settings and it now works perfectly. Sorry about all the wasted time everyone, and thanks for the help. -- Chris Green