Bug 937415 - UITour: Add ability to highlight the selected tab's icon in Australis. r=Unfocused

browser/base/content/tabbrowser.xml

@@ -4643,6 +4643,7 @@
                      role="presentation"
                      layer="true" />
           <xul:image xbl:inherits="src=image,fadein,pinned,selected"
+                     anonid="tab-icon-image"
                      class="tab-icon-image"
                      validate="never"
                      role="presentation"/>

browser/modules/UITour.jsm

@@ -64,6 +64,18 @@ this.UITour = {
       },
       widgetName: "search-container",
     }],
+    ["selectedTabIcon", {
+      query: (aDocument) => {
+        let selectedtab = aDocument.defaultView.gBrowser.selectedTab;
+        let element = aDocument.getAnonymousElementByAttribute(selectedtab,
+                                                               "anonid",
+                                                               "tab-icon-image");
+        if (!element || !_isElementVisible(element)) {
+          return null;
+        }
+        return element;
+      },
+    }],
     ["urlbar",      {
       query: "#urlbar",
       widgetName: "urlbar-container",
@@ -489,6 +501,10 @@ this.UITour = {
       highlighter.parentElement.openPopup(aTargetEl, "overlap", offsetX, offsetY);
     }
 
+    // Prevent showing a panel at an undefined position.
+    if (!_isElementVisible(aTarget.node))
+      return;
+
     this._setAppMenuStateForAnnotation(aTarget.node.ownerDocument.defaultView, "highlight",
                                        this.targetIsInAppMenu(aTarget),
                                        showHighlightPanel.bind(this, aTarget.node));
@@ -527,6 +543,10 @@ this.UITour = {
       tooltip.openPopup(aAnchorEl, alignment);
     }
 
+    // Prevent showing a panel at an undefined position.
+    if (!_isElementVisible(aAnchor.node))
+      return;
+
     this._setAppMenuStateForAnnotation(aAnchor.node.ownerDocument.defaultView, "info",
                                        this.targetIsInAppMenu(aAnchor),
                                        showInfoPanel.bind(this, aAnchor.node));
@@ -615,3 +635,8 @@ this.UITour = {
     aWindow.gBrowser.selectedTab = tab;
   },
 };
+
+function _isElementVisible(aElement) {
+  let targetStyle = aElement.ownerDocument.defaultView.getComputedStyle(aElement);
+  return (targetStyle.display != "none" && targetStyle.visibility == "visible");
+}