It would also have been a very public statement of position that he could have been held accountable to.
Go on.
Those who would have Christians deny Christ and embrace sin do the same: ergo anti-Christians should also lose their jobs?
Perhaps - but the question is silly - because there is no such thing as an anti-park-walker.
Just as I'm not so sure there is such thing as a serious 'anti-Christian'. People who suggest there is no God and call others stupid for believing in a God? Yes, they exist. But anti-Christians that would put money into a political campaign that seeked to change the law so that Christians were forced to deny Christ? No, I don't think those people exist in a any meaningful number.
Anti-gays that want to deny gays the right to marry - yes, quite clearly, they exist in large numbers.
He may have spent some time deciding to donate, he may also have made a snap decision and donated without consideration. You don't know. You also don't know how he spends his free time. You basically know nothing about him. I also know basically nothing about him, but I'm not making broad statements based on one piece of information.
The principle of presumed innocence has been completely ignored when it comes to Eich's personal life. His life is his to do with as he pleases (to an extent). I disagree with his position on gay marriage, I also think that the one data point coupled with his actions this past week say he probably shouldn't be CEO of Mozilla, but I don't know anything else about him, and can't, and shouldn't, make assumptions based on tiny morsels of evidence.
The only realm of Eich's life that I even microscopically care about (I really don't care all that much) is the public realm. As stated, I disagree with him, and think his selection to the CEO position probably wasn't considered enough, but that doesn't mean I'm fit to make comments on his personal life. Nor are you, unless you're closely acquainted with the man.