I think of Firefox the same way I think of Ubuntu. Both are technically FOSS but you can tell that their goals aren’t aligned with the end user’s. They certainly aren’t developed in the spirit of free software, just look at the crap they pull trying to monetise their “open source” products.
as the author of that article i obviously wouldn't disagree that there are serious problem with Moz, but my impression is that they are largely at the corporate level - the developers (at least some) seem to care far more about privacy which is why i personally recommend Firefox (along with a shit load of pref tweaks and a few add-ons) over any other mainstream browser, and especially G.Chrome
Mozilla is a Google subsidiary whose job is to support and perpetuate the illusion of competition.
Mozilla privacy policy is a lot like Google's --- sufficiently vague and opaque to allow them to violate user privacy whenever it's convenient.
this wouldn't surprise me, however... proof or go home