Edit:
makeee below posted a good source describing what Mozilla is currently doing, which appears to be limited to "researching" the problem of fake news.
I would love to support Firefox so I hope they come up with something more innovative than blocking (which they do not appear to be doing now - I stand corrected) or labeling (which has its own problems).
As I mentioned below, browsers, search engines, or social networks should not be, IMO, attempting to block or de-rank websites based on political activism, regardless of the source.