If you get this error while on a corporation (enterprise) intranet while trying to use Firefox:
Your connection is not secure
The owner of domain.com has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.
This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox may only connect to it securely. As a result, it is not possible to add an exception for this certificate.
then you need to activate this setting in about:config:
security.enterprise_roots.enabled = true
This is because your corporation is intercepting secure connections and it’s modifying them. So the message from Firefox is correct, your connection is not secure. By enabling this then you just trust the certificates used by your corporation so you must trust your corporation after enabling them.
In contrast everything works in Chrome but Chrome does not correctly inform you about the possible eavesdrop from your own corporation.