CONSOLE ERROR: Mixed Content: The page at 'https://127.0.0.1:8443/security/mixedContent/resources/frame-with-data-url-frame-with-frame.html' was loaded over HTTPS, but requested an insecure resource 'http://example.test:8080/security/mixedContent/resources/boring.html'. This request has been blocked; the content must be served over HTTPS.
This test opens a window that loads a data: iframe that loads an insecure frame, and that the frame is still blocked.