For one, he can't. Stallman can't arbitrarily change the license on another's work.
For two, if you look at the actual report, it's about the trademark of the Firefox logo, and Mozilla's right to decide what gets distributed under that trademark. They can fork all they want according to the MPL (not GPL, but closer to Sun's CDDL that you've praised), but they won't get the advantage of the brand recognition of Firefox.
Doesn't matter. He doesn't have to change the license to rip it, it's obviously already using a license that allows anyone to make free copies else these forks of Firefox wouldn't be appearing.
they won't get the advantage of the brand recognition of Firefox.
These forked versions will start replacing Firefox in many if not most versions of Linux by default. Stallman is "the father of free software", his leftist followers will quickly line up.