Riseup is absolutely with Mozilla's mission statement, though, and all things considered pretty good:

"Riseup provides online communication tools for people and groups working on liberatory social change. We are a project to create democratic alternatives and practice self-determination by controlling our own secure means of communications."

They have an actual anarcho-communist star in their logo and their website features revolutionary imagery and policy statements like "all labor is valued equally" and "the means of production should be placed in the hands of the people".[0]

I'm sure it's a fine organization if you subscribe to their views. I do not, and I'd rather not fund them, directly or indirectly.

[0] https://riseup.net/en/about-us/politics

I don't share their views, but I'm thrilled that their project exists and very happy with Mozilla donating to help improve their email client security, since it's a major player in the pro-privacy ecosystem. If I had to agree with the philosophical beliefs of everyone I gave money to, I'd starve.

If I donate to a FOSS project, I want the money to go into the development of their software and not turn into some proxy funding of other projects and organizations - especially not ones I disagree with. In fact, I think that's a pretty reasonable expectation.

I did not know about riseup (or Mozilla funding them) and parent provided insightful information about them. Given the funding structure of Mozilla, I could see this being a red flag for donations for some organizations/individuals.