Mozilla, much more than most is a political organisation (about freedom and openness) not just a commercial one. It has a mission, it will succeed with community support and goodwill. The political views of the CEO matter.
People are not saying (as far as I have heard) that there should be no place at Mozilla for Brendan Eich due to his political views but they are clearly uncomfortable with him leading a political organisation. A commitment and career somewhere does not entitle you to be CEO of the organisation if that is not what is best for the organisation.
> If anything the people criticizing Brendan Eich are trying to take away his freedom...
Freedom of speech isn't freedom from criticism, and criticism isn't censorship. Freedom of speech isn't freedom from social consequences for speech. Freedom of speech isn't an unconditional guarantee of employment.
Sometimes, freedom of speech becomes distasteful. I don't feel like this is one of those times, but I can understand why someone might disagree. In this situation, I see one person exercising their freedom of speech (in the form of a campaign donation) and a group of people responding with their own speech. That seems fine to me; if you disagree, could you elaborate on why, or describe what you think these employees should do instead? It seems to me that people responding to Brendan Eich should not have less freedom of speech than him.
Trading freedoms for employment is quite normal (my speech was constrained while employed - mostly about my company and it's products) but anyway Eich used his freedom which he is welcome to. However, having done that and expressed his political views (money is speech etc.) it should not be surprising that his political views are relevant to his ability in a political leadership role. If he can't take the community with him he is the wrong man for that role.
No, they're not. Freedom has to do with what the government is allowed to punish you for. No one is saying he shouldn't have been allowed to donate money in support of Prop 8. But actions have consequences outside of what the government can do.