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.
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.