This extensions sends a »Prefer: safe« HTTP header with every request, which signals servers your desire to avoid ”sensitive“ content. Servers supporting this feature should consequently only present content deemed ”safe“ by whatever standards they choose apply.
IMPORTANT: The actual implementation of the feature lies entirely in the hands of the content provider and totally *beyond* the perimeter of influence of this extension!
The »Prefer:« header has not been adopted by any standards organization yet, but is described in an IETF draft. It is currently e.g. supported by later versions of Firefox, which activates the feature behind the scenes in colaboration with the operating system's parental control settings.
 – https://blog.mozilla.org/privacy/2014/07/22/prefersafe-making-online-safety-simpler-in-firefox/