Telling your user-agent (browser) to use Polipo is an operation that
depends on the browser. Many user-agents will transparently use
Polipo if the environment variable http_proxy
points at it;
e.g.
$ export http_proxy=http://localhost:8123/Netscape Navigator, Mozilla and probably other browsers require that you configure them manually through their Preferences menu.
If your user-agent sports such options, tell it to use persistent connections when speaking to proxies, to speak HTTP/1.1 and to use HTTP/1.1 pipelining.