Há alguns anos, o W3C (World Wide Web Consortium) criou um mecanismo para os navegadores informarem aos servidores web que eles não gostariam de ser rastreados. Isso é feito incluindo um cabeçalho DNT (Do Not Track) com solicitações da web.
O cabeçalho DNT realmente não fornece nenhuma privacidade porque a maioria dos servidores da web o ignora. Por exemplo, Yahoo, Google, Microsoft e Facebook ignoram pelo menos alguns cabeçalhos DNT. A partir da versão 3.8, o Privacy Browser não tem mais a opção de enviar um cabeçalho DNT.
Privacy Browser removes tracking IDs and AMP (Accelerated Mobile Pages) redirects from URL queries. There is a blog post that is updated with the current list of modifications. URL modification can be turned off in the settings if it is causing issues.
Google programmed Android’s WebView to send an X-Requested-With header with every request.
The value of the X-Requested-With header is set to the application ID, which in the case of Privacy Browser is com.stoutner.privacybrowser.standard.
Currently, it isn't possible to remove this header, but the value can be changed. By default, Privacy Browser sends a null (empty) value for the X-Requested-With header.
Even though the spec allows for null header values, some web servers don't like them, so Privacy Browser has the option to revert to the default behavior of sending the app ID.
Because this setting is cached when a URL is first loaded, and isn't changed when reloading a page or navigating history,
changes to this setting may not be applied until Privacy Browser is restarted.
There is a blog post with additional information.
The X-Requested-With header will be completely removed in the 4.x series with the release of Privacy WebView.