The PropertyProvider::GetSpacingInternal function in Mozilla Firefox before 49.0 allows remote attackers to cause a denial of service (out-of-bounds read and application crash) via text runs in conjunction with a "display: contents" Cascading Style Sheets (CSS) property.
https://security.gentoo.org/glsa/201701-15
https://bugzilla.mozilla.org/show_bug.cgi?id=1288946
http://www.securitytracker.com/id/1036852
http://www.securityfocus.com/bid/93052
http://www.mozilla.org/security/announce/2016/mfsa2016-85.html