Mozilla just announced that all tests and related resources will be available
as public domain going forward and retro-actively for all tests for which
they own the copyright.
However, there's a lot of contributors here who own their own copyrights on
tests, and would need to license separately! Also, a lot of Mozilla employees
and contractors contribute under their non-mozilla.com accounts (which makes
it hard to tell they're covered) or have made test contributions before/after
working for Mozilla (which are not covered).