This extension is in early development state. Do not install it in a browser you actually use for anything. The extension is extremely intrusive and corrupts the security model of its host browser in many ways. The development happens publicly, so the current version is usually not in a state intended to be seen by an end-user. The functionality can be grouped into two categories.
In order to install the extension you can either download the Source folder and load it as an unpacked extension. Or you can download and install the irregularly updated packed CRX file from the Extension folder. There are no plans yet to support auto-updates.
The extension injects stylesheets and scripts into all visited web pages to block any sexual depictions either textual or graphical. In many cases it's forced to scrap security policies, so probably it's not safe to use on websites you either care for or don't trust. The image analysis might result in multiple downloads of the same image files.
This part of the extension isn't usable yet. It tracks the progress of the user by means of regular surveys etc.