Mozilla explicitly states that one of it's goals is to foster an inclusive and diverse software community. In their position, where they do so much work related to community engagement, do you not see how the views of their CEO conflicting with their stated mission is a problem?
If they're inclusive and diverse, then they should welcome people with different political perspectives. This isn't about tolerance and inclusiveness. It's about satisfying an angry, vindictive segment of the population that demands a sacrifice. Whether morally right or not, they have stepped in some deep doo-doo, and offended a broad swath of Mozilla supporters.
But I disagree that his personal opinions were incompatible with Mozilla. They make software, Eich makes software.
Mozilla has nothing to do with social activism. Well, at least, they didn't until now.