Mozilla's Firefox 3.6.7 [1] is a minor maintenance update that addresses a handful of security vulnerabilities and a long list of stability bugs. The 126 stability issues addressed in this update are minor and/or exceedingly technical, though if you'd like to peruse the list [2], it's available on Mozilla's Web site. The critical security vulnerabilities addressed could result in the standard threats of arbitrary code execution and attacker-controlled memory. More specific security notes [3] are available. Finally, the just-released 3.6.8 "fixes a single stability issue affecting some pages containing plugins." (Free, 17.6 MB)
[1]: http://www.mozilla.org/security/known-vulnerabilities/firefox36.html#firefox3.6.7
[2]: https://bugzilla.mozilla.org/buglist.cgi?quicksearch=ALL%20status1.9.2%3A.7-fixed,.5-fixed
[3]: http://www.mozilla.com/