Error code

Firefox SEC_ERROR_INADEQUATE_KEY_USAGE

FIREFOXSEC_ERROR_INADEQUATE_KEY_USAGE
Browser Error Code· An error code shown in a web browser when a page fails to load.

What it means

The certificate is being used for a purpose not permitted by its key usage extension.

How to fix it

  1. This is a server-side misconfiguration.
  2. contact the site owner.
  3. If you manage the server reissue the certificate with the correct key usage extensions.

Not affiliated with Firefox. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.