Are people suggesting that holding a personal opinion that is contrary to another person's opinion disqualifies that person from having a job?

I haven't seen any suggestions that he has attempted to discriminate, or implement discriminatory policies, against any individuals at Mozilla or otherwise.

I voted for Amendment 64 in Colorado to legalize canabis. Should that disqualify me from working because maybe means I get high too much (though I don't use)?

The argument against him is that he's discriminating, but now we have a case where OkCupid is literally and actively discriminating against users based on their choice of browser. Other people have actively threatened him. Those actions are, from my perspective, completely hypocritical: "We don't like people that discriminate, so we're going to discriminate against people that we don't agree with."