Код ошибки sec error inadequate key usage

Firefox was updated to v82.0.2 yesterday, and since then I’m getting this error using Firefox to connect to my NetGear ReadyNAS admin page, which uses the original self-signed certificate.
Secure Connection Failed

An error occurred during a connection to anemone. Certificate key usage inadequate for attempted operation. This is the error:

Error code: SEC_ERROR_INADEQUATE_KEY_USAGE

   The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
   Please contact the web site owners to inform them of this problem.

Learn more…

It doesn’t even display the certificate or give me the option to «Continue anyway». I have to use Chrome to connect, which make me even more unhappy!
With the previous version of FF, I could log into the admin page.
I should have the option to accept that the connection isn’t trusted, and continue to work. This NAS is in my home network behind a router and admin access is password controlled. That’s safe enough for my purposes.

I created a Blazor Server webapp and published it from Visual Studio using right click on the project — publish. I am publishing to a local folder, amongst others the output includes MyProject.exe
Running that works fine:

info: Microsoft.Hosting.Lifetime[0]
      Now listening on: http://localhost:5000
info: Microsoft.Hosting.Lifetime[0]
      Now listening on: https://localhost:5001
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Production

However I can not access my webapp on https://localhost:5001. Firefox gives me the error code SEC_ERROR_INADEQUATE_KEY_USAGE. There is no option to ignore it. Accessing it using Chrome just gives me HTTP ERROR 500. In the console where I started MyProject.exe I can find this error:

fail: Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware[1]
      An unhandled exception has occurred while executing the request.
      System.InvalidOperationException: Cannot find the fallback endpoint specified by route values: { page: /_Host, area:  }.
         at Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.DynamicPageEndpointMatcherPolicy.ApplyAsync(HttpContext httpContext, CandidateSet candidates)
         at Microsoft.AspNetCore.Routing.Matching.DfaMatcher.SelectEndpointWithPoliciesAsync(HttpContext httpContext, IEndpointSelectorPolicy[] policies, CandidateSet candidateSet)
         at Microsoft.AspNetCore.Routing.EndpointRoutingMiddleware.<Invoke>g__AwaitMatch|8_1(EndpointRoutingMiddleware middleware, HttpContext httpContext, Task matchTask)
         at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)
fail: Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware[3]

Can anyone help me with this? And yes, it’s a private application and shall run locally on localhost. When I run my webapp from Visual Studio, everything works fine.

I am provided CA Signed Server certificate, chain certificate and private key. From those, I created keystore using open SSL and secured the web application (HTTPS configuration in server.xml). However, when I tried to access web application via browser(Firefox), it gives out below error.

Secure Connection Failed
Certificate key usage inadequate for attempted operation. Error code: SEC_ERROR_INADEQUATE_KEY_USAGE

Certificates were initially in «.crt» and I tried after converting them to «.cer» as well. Still, the error complains something about «Key Usage». I ran following command to check certificate key usage and screenshot is attached.

openssl x509 -in ServerCertificate.cer -text -noout

Below is from Chain certificate;

Your help in resolving this issue is highly appreciated.
[PS: Before configuring CA signed certificates, I created self signed certs and that configuration worked with no issue]