Unfortunately that endpoint has an invalid certificate on it (hostname doesn't match)
Firefox does not trust this site because it uses a certificate that is not valid for deformdemo.repoze.org. The certificate is only valid for the following names: pylonsproject.org, static.pylonsproject.org, trypyramid.com, webob.org
The link to widget examples on https://docs.pylonsproject.org/projects/deform/en/latest/index.html leads to https://deformdemo.repoze.org/
Unfortunately that endpoint has an invalid certificate on it (hostname doesn't match)