Mozilla Firefox before 49.0 does not properly restrict the scheme in favicon requests, which might allow remote attackers to obtain sensitive information via unspecified vectors, as demonstrated by a jar: URL for a favicon resource.
https://security.gentoo.org/glsa/201701-15
https://bugzilla.mozilla.org/show_bug.cgi?id=932335
http://www.securitytracker.com/id/1036852
http://www.securityfocus.com/bid/93052
http://www.mozilla.org/security/announce/2016/mfsa2016-85.html