Pros
You can learn a lot from those real Mozillan: those who are really smart and understand what's good for open source and the vision of web. The dream and the insist on open web still so motivated. It's nice to hear those gurus to share the passion and vision with you.
Cons
Leadership and communication sucks. Also, lot's of people write horrible code without any design in mind, plus the extreme xenophobia to adopt other open technologies. As a result, even the code is under the correct license, it's still almost impossible to be useful for "community", not to mention other open projects. Ironically, it's also very unfriendly to new developers want to contribute. Obstacles from the legacy issue tracker to the "unique" CI services, and the architecture in chaos. So it's the most closed open source, and it looks like no one realize that and have the ability to make the real change. It's also very unacceptable that for the non-US offices, at least here, we've even been told "not to compare to US/other offices". There are many issues show that our opinions, no matter if they're about techs or welfare, we're expected to be suppressed and even ignored.