Import some fixes from Vimperator. Thanks anekos, teramoko, and stepnem.

common/modules/util.jsm

@@ -451,6 +451,16 @@ const Util = Module("Util", {
         return idx > -1 && idx + domain.length == host.length && (idx == 0 || host[idx-1] == ".");
     },
 
+    /**
+     * Returns true if the given DOM node is currently visible.
+     *
+     * @param {Node} node
+     */
+    isVisible: function (node) {
+        let style = util.computedStyle(node);
+        return style.visibility == "visible" && style.display != "none";
+    },
+
     /**
      * Returns an XPath union expression constructed from the specified node
      * tests. An expression is built with node tests for both the null and