bugs.torproject.org has some issue with the certificate

When I want to visit https://bugs.torproject.org/ Firefox says:

"Error code: SEC_ERROR_UNKNOWN_ISSUER"

OS: MacOS Mojave 10.14 Chrome https://share.riseup.net/#CYonUWZTp0NFD7xUGnqKwg Firefox https://share.riseup.net/#oGJLGO3dncEzfaqZfrEhFg