They actually do a good job at it, in my opinon. Also, Mozilla Corporation is still owned by the Mozilla foundation and aligned to their goals.

I didn't write that I don't want a corporate entity, I want a fully open product.

But while we're at it: Google is a corporate entity that did decide to keep development closed and showed their willingness to delay source code releases multiple times.

Mozilla (be it company or not) showed the willingness to keep everything in full open from the moment they announced the project.

This comes down to a question of governance.