diff --git a/layout/style/res/html.css b/layout/style/res/html.css
--- a/layout/style/res/html.css
+++ b/layout/style/res/html.css
@@ -744,16 +744,26 @@ video {

 video > img:-moz-native-anonymous {
   /* Video poster images should render with the video element's "object-fit" &
      "object-position" properties */
   object-fit: inherit !important;
   object-position: inherit !important;
 }

+div.foobar:-moz-native-anonymous {
+  color: red;
+  pointer-events: auto;
+}
+
+div.foobar:-moz-native-anonymous:hover {
+  color: green;
+  pointer-events: auto;
+}
+