JavaScript is something he produced, think of it as a work of art. The language itself doesn't portray his personal beliefs on topics other than language design. Putting him in charge of people who lifestyle he is not accepting of is different. It will influence the choices he makes in dealing with people and in how the organization behaves.

If the language had something like logging levels which were labeled by derogatory terms for a subset of people that'd be another issue but it doesn't.

Imagine if Ted Bundy had created a cure for cancer. Would you want to boycott it? Would you put him in charge of people? Now admittedly Bundy might be a bigger danger to a specific subset of people than Eich but Eich is still a danger in some way to a subset of people.

Boycotting FireFox isn't about the product, it is about sending a message to the organization that puts him in a position of power over people.