Mozilla Firefox before 20.0 on Android uses world-writable and world-readable permissions for the app_tmp installation directory in the local filesystem, which allows attackers to modify add-ons before installation via an application that leverages the time window during which app_tmp is used.
https://bugzilla.mozilla.org/show_bug.cgi?id=844832
http://www.mozilla.org/security/announce/2013/mfsa2013-33.html
http://lists.opensuse.org/opensuse-security-announce/2013-04/msg00013.html