Mozilla Firefox before 41.0 does not properly restrict the availability of High Resolution Time API times, which allows remote attackers to track last-level cache access, and consequently obtain sensitive information, via crafted JavaScript code that makes performance.now calls.
https://bugzilla.mozilla.org/show_bug.cgi?id=1167489
https://bugzilla.mozilla.org/show_bug.cgi?id=1153672
http://www.securitytracker.com/id/1033640
http://www.mozilla.org/security/announce/2015/mfsa2015-114.html