https://marketplace.firefox.com/developers/validator is behind authentication right now. I think we did that long ago on AMO because it was slow but we're bigger and better now. Let's open it up.
We'd need to change the API to not require auth as wel.
Basta tried - but to no avail:
1) Go to https://marketplace.firefox.com/developers/validator
2) Enter a manifest URL or packaged app.
3) The POST results in a 403 because you're anonymous, and there's no anonymous_csrf token.
We currently advertise the App Validator on https://marketplace.firefox.com/developers/docs/ so this may be a problem.
verified fixed at https://marketplace-dev.allizom.org/developers/validator