Quote:Privacy-Oriented Origin Policy is anew browser extension for the Firefox web browser that blocks Firefox from sending Origin headers under certain circumstances.

To understand what Privacy-Oriented Origin Policy does, it is necessary to understand how the same-origin policy and cross-origin resource sharing works.

The same-origin policy is a security model that restricts access to resources, e.g. JavaScript scripts, based on the origin (made up of scheme, hostname, and port); this is done to prevent cross-site scripting and cross-site request forgery attacks.

Cross-Origin Resource Sharing bypasses the same-origin policy so that other sites may request resources protected by the same-origin policy.

When a browser makes a cross-origin resource request, it adds a reference to the HTTP header that includes the origin that triggered the request. In other words: it tells the server the request is made to that you came from a certain domain, e.g. https://www.example.com:8080.

Privacy-Oriented Origin Policy may modify these requests to block the information from being revealed to the site the CORS request is made to.

The extension comes with several modes of operation; the default mode, relaxed, relies on heuristics to determine whether it is save to strip the origin header. Aggressive mode on the other hand strips all origin headers. Both modes work on GET requests only.

Relaxed mode won't remove the origin header if the request includes cookies, authorization header, or username, password, query, or hash data in the URL.

Full reading: https://www.ghacks.net/2019/01/19/privacy-oriented-origin-policy-for-firefox/