How to change Firefox's referer header for all http requests
The Firefox add-on RefControl can do this.
It has an option to always replace the Referer with the host only (stripping of the URL path). So if the real Referer is http://example.com/foo/bar.html, it becomes http://example.com/.
network.http.sendRefererHeader is Firefox option to control Referer header.
There are also some extensions like refspoof or "No Referrer".