masking warnings like 404 error and display a blank page instead of the error

I have a requirement where instead of showing the 404 error or 503 error on screen, I want to display a blank screen. I have already tried to set the following configs to false - security.insecure_connection_text.enabled security.insecure_connection_icon.enabled security.insecure_connection_text.pbmode.enabled browser.ssl_override_behavior security.ssl.errorReporting.automatic security.enterprise_roots.enabled security.tls.version.min Is there anymore steps to do or any userChrome.css script is required. PS : I cannot use any extension or addon to do that