Step back and see the bigger picture, will you? Mozilla has a lot of power in that their browser is used by a whole lot of people. Is that a group that should take sides on political issues? Protecting free speech should be their absolute number one priority. No one wants a web browser or mail reader that has ideologues controlling it. Would you use a web browser pushed by the NSA?
It's true what you say about free speech, and it does have consequences. Chrome got a lot of new users out of this, ironically. Ousting a CEO for one donation many years ago when even the President of the USofA believed the same at the time is a bit absurd. You raise an interesting point too. He was fired over information that should never have been released. That just makes it that much worse.
Think about the shoe on the other foot. What if companies started firing people for donating to some issue you care deeply for? Prop 8 is a side show here. This could have been about any issue, left or right. I'm not in favor of going after people in the workplace for what they believe in their personal life. If he was supporting NAMBLA, that's one thing. But this is a contentious issue, one of many. We need conversation, not condemnation. Forcing silence for fear of losing one's profession is horrible. That's not American.