People naturally feel anger in their lives (about home, work, politics, health, etc.) that is not socially acceptable to act on; to varying degrees, they need an outlet. It's not a new phenomenon; some go to the gym or play video games (where some act out on audio channels); some people drink heavily; some abuse people close to them, or the waitress, or get in a fight at the bar, or join an angry mob and lynch someone in the streets. When there is a socially acceptable target, indicated by lots of other people acting out, they act out too.
Changes like Firefox's attract outrage not because they are wrong but because they create a social attack surface: People can see that the change isn't socially secure (e.g., messages about inclusiveness are relatively secure right now[0]) and thus know that it will be a target for attacks; again, it's socially acceptable. They attack because it's a vulnerable target; there is chum in the social waters.
Consider how much of such outrage completely disregards the facts and betrays a lack of interest in learning the facts. They make no effort to learn about the facts - I see almost no discussion of the merits or facts on this page - and you can put the information in front of their eyes and they will ignore it and attack you: by not joining them you expose your own social vulnerability.
It's very dangerous socially; mass bullying campaigns have serious, real effects on their victims. Whole nations embrace bad policies, from discrimination against their own to war, that can kill in the hundreds of thousands or more and ruin generations. Evil leaders manipulate this phenomenon.
But also consider the affect it has on innovation, something we should be very concerned about at HN. It stops innovators from getting too far ahead of what's already accepted; they will be judged by their social security not its merits. It kills innovations from those who are socially acceptable; for example, the Blackberry Passport was the most innovative phone in years, but it was trashed, including on HN, because Blackberry Inc. was socially vulnerable, an outcast.
If you read this far, thanks for listening!
[0] To be clear, I'm not disparaging them - I strongly support them.