An activist organization that is so intransparent that I don't even get what they are activists for.

I have only ever recognized blog posts about interpersonal matters by them which are rather cringy and don't add anything to the preexisting matter. All about first world problems.

Do you happen to know what concrete and half effective activism they actually do?

I don't know if any of it is "half-effective" but it's the standard social-justicey things like "women and BIPOC in tech", as well as more recently, alerting people to the dangers of the open internet and pressuring platforms to take more aggressive censorship actions: https://blog.mozilla.org/en/mozilla/we-need-more-than-deplat...

I think Mitchell Baker would rather chair something like the SPLC than an organization merely devoted to the development and maintenance of open source software, and that's what she's turning Mozilla into.

I think they were one of the main drivers behind let's encrypt and maybe some other stuff so all is not wasted.

My main criticism is that they "milk the cow dry" by extracting so much money from the browser (which is their single largest source of income) that it starves.