"Bug 846489 - Create an SSL Error Reporting Mechanism" allows users to e.g. report server key pinning mismatches. Firefox forked the about:neterror page for its new style in bug 982347. Set security.cert_pinning.enforcement_level to 1 and open https://pinningtest.appspot.com/ to get a demo of the feature. If you want to open a content tab in Thunderbird with the site, run the following code in Scratchpad while remote debugging: document.getElementById("tabmail").openTab("contentTab", {contentPage: "https://pinningtest.appspot.com/"});