Trying to prevent someone from retaining their high-paying job at a company I do business with after they donate heavily to the KKK is not bad.
Trying to prevent someone from retaining their high-paying job at a company I do business with after they buy ingredients for a grilled cheese sandwich is bad.
Trying to prevent someone from retaining their high-paying job at a company I do business with after they have given money to an anti-marriage-equality campaign is...?
Well, that's the one question that's actually being debated here. Your inability to recognize that the three are different makes the debate harder, to be sure, but that remains what the actual disagreement is about.
Your phrasing is mistaken. Here's an amendment:
Trying to get someone fired from their high-paying job at a company I do business with, after they are appointed, having once donated heavily to the KKK is ???
Trying to get someone fired from their high-paying job at a company I do business with, after they are appointed, having once bought ingredients for a grilled cheese sandwich is ???
Trying to get someone fired from their high-paying job at a company I do business with, after they are appointed, having once given money to an anti-marriage-equality campaign is ???
I'm frankly not sure about the moral relevance of the "high-paying" part. Would you have allowed him to stay on if he'd agreed to take $1 annually as compensation? (and no tricks wither - straight up, he does the job and what he gets is a buck a year) If not, then the "high-paying" part can get removed.
Also, I think it's unlikely that you "do business with" Mozilla in any meaningful sense. If you're a typical user, you take something that they make, and use it. Is that "doing business"? I don't know, but it doesn't sound like it to me. I suppose you do have a license agreement with them, since you clicked the little button to install the software. But of course, I don't know how relevant that is. Just to make sure it gets said: you almost certainly have no financial stake in this. The arguments made earlier (by others) about "giving your money to a bigot" were even more ludicrous than usual in this case, because the end user gets the product for free. So I think that clause can go as well.
Finally, we might want to make it clear that in all cases, the offense in question was well known by those charged with hiring the offending party, and those people considered the offense, and it did not sway them to decline to hire him, and that no new offense has been brought up. So we're talking about exactly one offense, which has already been considered and the candidate accepted anyway. And, to be fair, let's also point out that in none of the cases has the target of our ire expressed remorse or regret for their act.
I'm happy to consider these cases, but I want to make sure we're talking about the right story. I think that these modifications get us closer.
So when I look at your cases, the main moral difference is that the KKK is an organization devoted to murder and terrorism, the Prop 8 campaign is devoted to electoral politics, and the cheese sandwich has high cholesterol. That seems like we're comparing apples and oranges and, well, sandwiches. In my view, everyone has the right to take part in election campaigns, assuming compliance with the applicable laws. The KKK candidate's donation was not an act of political participation, it was a donation to a terrorist group. I do not see that contributing to terrorism is a right that I think people should have and that we should respect, so I don't see that there's an ethical problem with trying to punish someone for that if you should choose to do so. On the other hand, the Prop 8 donation was an act of political participation, and I think it is immoral to organize to try to punish someone for exercising that right. So I think it is not bad to try to get the KKK guy fired for contributing to support terrorists, and I think it is bad to try to get the Prop 8 guy fired for contributing to support a repulsive ballot proposition.
And the guy with the grilled cheese sandwich makings should make me one. And a bowl of tomato soup.