A few things: It all started when they ousted Brendan Eich over some controversial political donations. I don't agree with this decision but Mozilla was catching a ton of bad PR so it was probably the only option. Right wing types have had a hateboner for Firefox ever since. For technically minded people, Mozilla lost a lot of credibility when they laid off many engineers working on innovative projects like Servo. Firefox development has been stagnant ever since, and they rarely push new non-cosmetic features.