Why? Because Brendan Eich had donated $1000 in support of Proposition 8, which attempted to block marriage equality by inserting the language from Proposition 22 (ruled unconstitutional in 2008), namely "only marriage between a man and a woman is valid or recognized in California", into the California Consitution.
The information regarding Eich's donation had originally come to light back in March 2012, and had been controversial at the time.
Mozilla and Eich's comments on the situation:
Mozilla[/url]]Q: Was Brendan Eich fired?
A: No, Brendan Eich resigned. Brendan himself said:
“I have decided to resign as CEO effective April 3rd, and leave Mozilla. Our mission is bigger than any one of us, and under the present circumstances, I cannot be an effective leader. I will be taking time before I decide what to do next.”
Q: Was Brendan asked to resign by the Board?
A: No. In fact, Board members tried to get Brendan to stay at Mozilla in another role. Brendan decided that it was better for himself and for Mozilla to sever all ties, at least for now.
Brendan Eich[/url]]I’ve resigned as CEO and I’m leaving Mozilla to take a rest, take some trips with my family, look at problems from other angles, and see if the “network problem” has a solution that doesn’t require scaling up to hundreds of millions of users and winning their trust while somehow covering costs. That’s a rare, hard thing, which I’m proud to have done with Firefox at Mozilla.
bandit0013 had raised concern that Eich's political views led to his dismissal, and NormanTheIntern seemed to want to make the argument that this was an instance of "mob justice" and that there was a clear moral hazard here (though his comparisons to the blacklisting of atheists and socialists did muddy the waters a bit).
It's derailing the Prop 8 / Gay Marriage thread, so I'm creating this one for that conversation to continue.