Mozilla Firefox before 3.6.24 and 4.x through 7.0 and Thunderbird before 3.1.6 and 5.0 through 7.0 do not properly handle JavaScript files that contain many functions, which allows user-assisted remote attackers to cause a denial of service (memory corruption and application crash) or possibly have unspecified other impact via a crafted file that is accessed by debugging APIs, as demonstrated by Firebug.