I think it's probably a combination of both. There's an astroturfing campaign going on somewhere, just not on Lemmy, which is overall too small and insignificant to target. But astroturfing works - it creates the echo chambers you're talking about, it creates apathy. Most people just read headlines, not even the comments. You read a bad story about Mozilla once a week and you'll start to internalize it - eventually your opinion of Mozilla will drop, justified or not, to the point where you're willing to believe even the more heinous theories about it.
So you end up with a lot of people who've been fed a lot of misleading half-truths and even some outright lies, who are now getting angry enough about the situation they think is going on to start actively posting anti-Mozilla posts and comments on their own.