Bug#962564: getting "Forbidden (403) CSRF verification failed. Request aborted. More information is available with DEBUG=True." with Firefox from buster

Package: sso.debian.org
Severity: normal

When I try to "get certificate via Certificate Signing Request"
via https://sso.debian.org/debian/certs/enroll_csr/ with Firefox-ESR
(68.9.0esr-1~deb10u1) from Debian buster, I get a:

    Forbidden (403)
    
    CSRF verification failed. Request aborted.
    
    More information is available with DEBUG=True.

Cookies are on. JavaScript is on.

?
*t

-- System Information:
Debian Release: 10.4
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.19.0-9-amd64 (SMP w/8 CPU cores)
Locale: LANG=de_CH.utf8, LC_CTYPE=de_CH.utf8 (charmap=UTF-8), LANGUAGE=de_CH:de (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled