Bug 1572019 - Give the new protection panel an accessible name r=johannh

Differential Revision: https://phabricator.services.mozilla.com/D40950

--HG--
extra : moz-landing-system : lando

browser/components/controlcenter/content/protectionsPanel.inc.xul

@@ -7,6 +7,7 @@
        type="arrow"
        hidden="true"
        role="alertdialog"
+       aria-labelledby="protections-popup-main-header-label"
        onpopupshown="gProtectionsHandler.onPopupShown(event);"
        onpopuphidden="gProtectionsHandler.onPopupHidden(event);"
        orient="vertical">