I think when there's overblown criticism (does not take into account the positive things, seeks only to paint in a negative light), that's pretty clearly FUD.
Moreover, when there's a pattern of it occurring, for at least the past 5 years...
Not saying that firefox is perfect, I have issues with its project leadership too, but its nowhere near as bad as the (most vocal) critics like to claim.
"This is a problem, and here is what I/we should do", takes a bit more effort.
Firefox is still open source last I checked. You can still contribute, write bugs, write letters to the CEO, etc...
I'm only taking issue with tendency people have to throw shade without offering a solution.