Mozilla have been doing odd things in recent years, almost like they are transitioning into an authoritarian movement. Want to use unsanctioned extensions? No, go away. Want to use non-secure HTTP? Sure, but we will take away your features. Want to work for them but have unapproved views? Fired. All this is from viewing them as an outsider, so you never know, but something is different.
There was a large outcry, then he resigned. His resignation can be directly traced to his views. Whether he was technically fired or "decided" to resign seems largely irrelevant.