Firefox 70 added a new „Certificate Viewer“ feature which moves the „Window“-based GUI to a „Web-Page“-View.
- different look
- no new features
- missing features
- Export Certificate
So this is no „new feature“ but a „modification of an existing feature“ – with less features.
Reenable the former full featureset
about:config
security.aboutcertificate.enabled := false

Disclaimer
Since i’m trying to get rid of Evernote, too anoying too often, i’ll start to document non-private-stuff here.