It looks like 4 years ago Firefox added a system to centralize the addons and only allow ones pre-authorized by Mozilla. Mozilla then became a central authority determining the legitimacy of an addon.
That pretty much knocks out Freedom Zero with regard to Firefox: the freedom to run the program for any purpose.
@bob not exactly, you can always enable addons which aren't signed by Mozilla and run them without anyone's approval on your browser. Also you can change the source code and build in any extension you want. That's how TOR browser was created.
@nedelne_rano It depends how the browser was compiled. There's a flag which just hardcodes that all addons must be signed by Mozilla, and I think this is why yesterday some people were saying that they've tried the about:config twiddling but it didn't work.