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.