I had four hangouts interviews in total: one with HR, one with a manager and two with security team members. As someone wrote already phone interviews weren't too technical, it looks like Mozilla is more interested in how you fit the team. There was supposed to be an onsite interview at some point, but they became silent for 4 weeks after the last call. Then I got an email I wasn't accepted. That's OK, but somehow I felt I was kept for a month without a notice as a backup plan if the onsite candidate failed. I asked HR for a feedback. No reply received.