Thank you for the report, @Veruska.
We have a ticket in our backlog to address this and improve the SSL/TLS workflow in general, but I don’t yet have a timeline for the fix.
For the issue under Chrome, you can try removing the certificate from Keychain Access and re-adding it following the certificates guide for macOS. For me, this gives a secure cert chain:
The issue under Firefox is a known problem that our planned updates to cert generation are expected to fix.