Mozilla released an update for Firefox to fixed a serious flaw allowing remote access to local files.
Visiting a malicious website could allow an attacker to access files on the victim’s local file system. The vulnerability is being actively exploited on Windows, Mac, and Linux systems.
The vulnerability has been fixed in Firefox 39.0.3 and Firefox ESR 38.1.1
Firefox should be updated as soon as possible and of course only visit trusted web sites.
Additional information an be found at
https://www.mozilla.org/en-US/security/advisories/mfsa2015-78/
https://blog.mozilla.org/security/2015/08/06/firefox-exploit-found-in-the-wild/