Mozilla Firefox before 44.0 on Android does not ensure that HTTPS is used for a lightweight-theme installation, which allows man-in-the-middle attackers to replace a theme's images and colors by modifying the client-server data stream.
https://security.gentoo.org/glsa/201605-06
https://bugzilla.mozilla.org/show_bug.cgi?id=1235876
http://www.securitytracker.com/id/1034825
http://www.mozilla.org/security/announce/2016/mfsa2016-12.html