Changes

[http://valgrind.org/ Valgrind] is a free tool for Linux and Mac that detects various kinds of memory-related errors at runtime, including leaks. Documentation on how to use it with Mozilla code is [https://developer.mozilla.org/en-US/docs/Mozilla/Testing/Valgrind here]. Valgrind is used as [https://developer.mozilla.org/en-US/docs/Valgrind_test_job part] of Mozilla's continuous integration testing, though the coverage isn't great is limited because Valgrind is slow.