CONSOLE ERROR: line 8: Mixed Content: The page at 'https://127.0.0.1:8443/security/mixedContent/resources/frame-preloads-insecure-image.html' was loaded over HTTPS, but requested an insecure image 'http://example.test:8080/security/resources/compass.jpg'. This request has been blocked; the content must be served over HTTPS.
This test opens a window that loads an insecure image. We should not trigger a mixed content callback even though the main frame in the window is HTTPS and is displaying insecure content, because we've set the preference to block this.