Error "Secure Connection Failed" SEC_ERROR_INADEQUATE_KEY_USAGE
From the last week Firefox started to give me the error "Secure Connection Failed" / SEC_ERROR_INADEQUATE_KEY_USAGE, preventing me to access some intranet sites. The first time I tried the "Refresh Firefox" procedure found at the beginning of the dis-installation function (started through the standard "Add or remove programs" Windows 11 interface). Now this error re-appears only for one of the internal sites from time to time. If I close all the browser windows and re-open Firefox, the error changes to "Warning: Potential Security Risk Ahead" / MOZILLA_PKIX_ERROR_SELF_SIGNED_CERT (which is an error I'm expecting since the intranet site is using an intenal Certification Authority that I've not yet put among the trusted ones) and with this message I can now proceed to the site by selecting "Advanced..." and "Accept the Risk and Continue".
Which is the reason for SEC_ERROR_INADEQUATE_KEY_USAGE error? I cannot find a mention for it inside https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean ... Is there a way to debug it? Or to avoid re-occurring and the need to restart Firefox?
Firefox version is "113.0.2 (64-bit)" on Windows 11 (10.0.22621.1702).