You think it is done by holding feminist AI conferences in Africa?

Yes, that's part of it. Guys in SV don't need help with access; women in Africa do - that's the place to hold conferences, and probably much more cost effective. (Whatever is mean by 'Africa', a very large area, and I know nothing about the conference.)

Yeah, but what would be the most optimal way to achieve the goals (spreading an open web)?

If we start with the propostion that all people are created equal, and have equal value, then adding some marginal value in SV seems to have lower ROI than transforming lives in a place where people have little access to the resources and people of the IT industry. And in many societies, women face discrimination that tries to exculde them from tech.

Intel isn't hosting a hardware conference in 99% of the world. It's a great opportunity for Mozilla's mission, for those people, and for the world.