Pros
Work-life balance, remote work. Nicely located offices. Open source. Good if you have a family.
Cons
Heavy corporate culture. Full of corporate middle managers with not much to do. Expect many meetings with product managers, engineering managers, project managers, strategy managers, with one developer to solve simple problems. Politics and diversity are superficial; they use diversity as a card when it suits them, and ignore it otherwise. Leadership is a boys club of friends from the old days from dead companies that hire each other. They might reject a good hire and play the diversity card, and then go around and hire ten non-diverse people. Succumbed to the big players. No longer innovative and low ambition. Good ideas shot down due to fear of Google. Strategy revolves around corporate partnerships and lots of managers. Weekly meetings focus around trying to convince people that Mozilla is doing OK. Successful projects when noticed will be swarmed by managers trying to advance their careers. If you do something good, expect to later be pushed out. Successful and driven people get their bonuses docked by managers because they speak up. If you grow a flower, expect it to be picked and killed. Office politics and bullying. People lobbying managers and ostracizing good people. Emotional abuse will make you lose your sanity. Safe haven for slackers. Developers that have done nothing for months or years. Perhaps they change a config file once every two weeks. Developer culture is gone. Most developers stay around because they have families to feed. A lot of the developer-oriented media are low quality article and speaker factories.