In about:config, setting 'network.http.sendRefererHeader' to 0 (default is 2) will stop the referer header from being sent, and the document.referrer from being set. See http://kb.mozillazine.org/Network.http.sendRefererHeader for more information.
https://raw.githubusercontent.com/pyllyukko/user.js/master/u...
user_pref("network.http.referer.userControlPolicy", x);
// TODO: https://github.com/pyllyukko/user.js/issues/94, commented-out XOriginPolicy/XOriginTrimmingPolicy = 2 prefs
user_pref("network.http.referer.spoofSource", x);
user_pref("network.http.referer.XOriginPolicy", x);
It seems that Firefox 59 will effectively force about:config's network.http.referer.XOriginTrimmingPolicy to 2 (default is 0) when in private browsing.
In the URL bar, type:
about:config
Search for the following setting:
network.http.referer.spoofSource
Double-click to set its value to true. This basically sends the destination or target URL as the referrer.
Description: "If a page hasn't set an explicit referrer policy, setting this flag will reduce the amount of information in the 'referer' header for cross-origin requests."
Configurable referer behavior, including whitelist.