In California, where Mozilla is headquartered, political views are a protected class. It's not (in principle) legal for an employer to fire you for your off-the-clock political views.
Honestly, I think the most applicable courses to that situation are civics, logic, and law. Civics to make you realize how important it is to get the actual facts of the situation, logic to understand what they mean, and law for numerous applications of those two learnings.
In this case, the most relevant part is whether Eich was fired. As far as can be determined externally, he was not. Depending on your leanings, you may decide to believe (perhaps based on evidence, perhaps not) that what probably happened was morally equivalent to being fired -- but again, logic and law say that doesn't matter. If the law says you can't do X when condition Y holds, but Y is kind of blurry and hard to determine precisely, then all that means exactly nothing if you didn't do X.
Feel free to debate the legality or the ethics, but please don't get them mixed up.
On the contrary, respecting the intent of the law is a critical component of corporate ethics. If the people of California say that companies shouldn't control their employees' politics, but I don't like that rule so I find some loophole to do it anyway, I'm behaving unethically.
