about:config:

• network.http.sendRefererHeader
  0 - never send the referring URL.
  1 - send only when links are clicked.
  2 - send for links and images (default).

• network.http.referer.XOriginPolicy
  0 - always send referrer (default).
  1 - only send if base domains match.
  2 - only send if hosts match.

• network.http.referer.spoofSource
  false - send the referrer (default).
  true - spoof the referrer and use the target URI instead.

• network.http.referer.trimmingPolicy
  0 - send full URI (default).
  1 - scheme, host, port and path.
  2 - scheme, host and port.