A Proxy allows the machine your Grail Browser is running on to reach the Internet through a Firewall running an HTTP Proxy service. HTTP Proxy Servers such as CERN's httpd server typically run on a special port (the default configuration is port 8080) other than the default port 80, and transparently pass your requests to Internet servers outside of your private network. Generally speaking, once a Proxy service is configured, as a user, you are unaware that it's acting as a relay for your web traffic.
Grail currently supports proxying for the http and ftp protocol schemes. Both of these schemes are proxied via http, which is somewhat counter intuitive.
To enable proxy capability within Grail, select the Manual Proxy Configuration button. You should see the http and ftp proxy server buttons become enabled. One at a time, select the proxy you wish to configure by pressing the newly enabled button on the left and typing in your proxy URL in the entry field to the right. A proxy URL is of the form:
cnri.reston.va.us, .python.org, www.ftp.org
Proxy support in grail can also be configured using environment variables. The following environment variables replicate the function of the proxies preferences panel and have the side effect of updating preferences to match: