Uneasy way to determine proxy server

Open a command prompt and perform the following steps:

1. Inspect the output of netstat -an | find "EST" (short from 'ESTABLISHED')
2. Go to a fresh site (one that you have not recently visited)
3. Run the netstat command again, looking for the new connection. It might look like:
   TCP 192.168.1.1:1989 192.168.1.88:8080 ESTABLISHED

(credits go to Royce Williams)

Alternatively, install TCPView and look at the remote address and remote port columns for the browser connections.