I'm aware of a research project to see if reliable identification of "fake news" websites is possible, but there's no "blocking" coming to Firefox. That would violate point 5 of the Mozilla Manifesto.
That would violate point 5 of the Mozilla Manifesto.
They can interpret that however they want. For example, you can always "shape the Internet and [your] own experiences on it", including removing any blocking, adding things they remove, etc... just get the source code for Firefox and make all the changes you want.
It's all a bunch of vague marketing doublespeak anyway, with around as much power over what Mozilla does as the US constitution has on the US government.
https://www.mozilla.org/en-US/about/manifesto/