Security error (i.e. SEC_ERROR_INADEQUATE_KEY_USAGE)
All. The answers to all the issues with security errors like SEC_ERROR_INADEQUATE_KEY_USAGE end up with "contact the web owner". In many cases for me, these web sites are not internet sites but hardware HTTP servers (e.g. like a system's BMC or iLO) and there is no system administrator to contact. The web sites open up fine in Chrome. There has to be other solutions (like setting an exception) to work around these issues. Eddy
There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.
Websites don't load - troubleshoot and fix error messages
I don't find a solution in any of the links that you supplied. What else can I do? Do you need some log files from my browser? Eddy
There are several things to try.
Delete the cert9.db file.
Type about:support<enter> in the address bar.
Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.
Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
Linux: Under the page logo on the left side, you will see Application Basics. Under this find Profile Directory. To its right press the button Open Directory.
Locate the above file. Then rename or delete it. Restart Firefox.
Do these pages work if you use the http:// protocol ?
You can disable HTTPS-Only mode by clicking the padlock icon in the location bar and disable HTTPS-Only for this origin (protocol and hostname).
If that doesn't work then you will have to HTTPS-Only in Firefox.