Two details: the extensions need to be signed by Mozilla, and only US English speakers will be allowed to disable this requirement.
The point of free software is that users, individually and collectively, are free to modify it as they wish, without requiring approval from third parties. (And of course to use, copy, and redistribute.) This is a sharp turn away from the free-software ethos that made Firefox possible in the first place.
I understand the issue of users being tricked into downloading and installing malicious extensions. If you let someone program, they will be able to paste malicious code. I just don’t think that taking away users’ ability to modify their own browsers is an acceptable solution to that.
If this disturbing move sticks, Mozilla will become an increasingly tempting target for whatever group wants to control what software you can install on your own computer — whether that’s Sony Pictures, the NSA, or Amazon.
The old free software movement has died. We need a new free software movement.