If you get this error (NS_ERROR_NET_INADEQUATE_SECURITY) when visting HTTPS site on Firefox, that means the web server has something wrong with SSL certificate (old ciphers, lower TLS version).
Here is how to fix your Firefox to access that page:
- Open Firefox and type about:config in the address bar
- Click on I accept the risk button
- Type http2 in search box
- Find network.http.spdy.enabled.http2 and double click to make it false (to disable http2).
That’s all. You may need to close Firefox and reopen it.
Hope it helped you. 🙂