So—just out of this subset of expenses, there's probably some other stuff you could take issue with—Mozilla spent money in a 94% ratio on browser development, and 6% on "other stuff", of which probably .001% was this conference in Africa. And I think it's arguable that a lot of that "other stuff" is related technology! But even ignoring that, talking about how we can use the open web to improve life for people in third world countries is exactly the kind of thing that I, personally, would like Mozilla to be doing. And I'm happy for them to spend <5% of their budget on it.
Only because you assume that they should only be working on browser development.
Why not? This isn't Oxfam, this is Mozilla. To an outsider, the assumed point for all these other endeavors was to be profitable to provide more money for browser development. When that money doesn't primarily provide for that something seems sketchy.