It's actually not that crazy for the skills they are looking for. Looks like they are looking for more of an old school "web master" than a software developer. Plus the generous (by US standards) benefits and I'm guessing a very relaxed work environment. Plus you get to actually spend time toward doing good in the world.
Web developer: https://www.fsf.org/resources/jobs/fsf-job-opportunity-web-d...
Copyright/licensing associate: https://www.fsf.org/resources/jobs/fsf-job-opportunity-copyr...