The accessibility-tools feature in Mozilla Firefox before 42.0 on OS X improperly interacts with the implementation of the TABLE element, which allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code by using an NSAccessibilityIndexAttribute value to reference a row index.
This entry has been deprecated. It was originally used for organizing the Development View (CWE-699) and some other views, but it introduced unnecessary complexity and depth to the resulting tree.