It's dangerous, however, to allow an employer with "mission fit" to get away with things you wouldn't take from another employer.
For instance, in recent years, in the US, we've taken a hard stance that interns who perform essential job functions - which basically all interns do - must be paid. Should this requirement be relaxed for a non-profit? How does the way I feel about that change if I'm a donor to that non-profit? I care about the mission, but I also care how we get there.
I'm fairly sure that internal to Mozilla, Wikimedia, ahem the Association for Computing Machinery (promoting computing as a science AND a profession!), and any other non-profit corporation you can find a lot of the same internal struggles that employees everywhere face.
Further, you have a leadership team who believes it's OK to pay people below market because they "love" and "are loyal to" their job.
It works for a lot of people, and I know / have known a lot of folks very happy with such choices, but it can be a dangerous alleyway to wander down as well.