When a new Firefox profile is created on 64-bit Windows installations, the sandbox for 64-bit NPAPI plugins is not enabled by default. Note: This issue only affects 64-bit Windows. 32-bit Windows and other operating systems are unaffected. This vulnerability affects Firefox < 50.
https://www.mozilla.org/security/advisories/mfsa2016-89/
https://bugzilla.mozilla.org/show_bug.cgi?id=1300083