This is a regression. https://people.mozilla.org/~tvyas/windowopen3.html This page does a window.open('about:blank'). And then populates mixed display and mixed active content on the page. The active http script is blocked with no way to unblock. In Firefox 41, you see a shield icon on the about:blank page letting you disable protection. The security UI on the original page doesn't change in any version, as far as I can tell. The green lock remains on the people.mozilla.org tab when mixed display or mixed active loads on the about:blank page. the about:blank page gets a globe icon regardless. the globe icon is not clickable. We can discuss whether or not we want to handle this edge case.