Privoxy

Privoxy is a web proxy with advanced filtering capabilities for enhancing privacy. Privoxy can be paired with Squid to provide filtering to it.

Emerge
To install Privoxy:

OpenRC
To make privoxy start at boot:

Configuration
The default file for configuring Privoxy is

Test filters
There is a way to test the filters that are applied to a specific site.

If privoxy is working correctly the next URL should be intercepted by privoxy.

http://config.privoxy.org/show-url-info