diff --git a/src/Add-ons/Addon.cxx b/src/Add-ons/Addon.cxx
index ee6686db0..895ed2138 100644
--- a/src/Add-ons/Addon.cxx
+++ b/src/Add-ons/Addon.cxx
@@ -17,6 +17,7 @@
 // with this program; if not, write to the Free Software Foundation, Inc.,
 // 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
+#include <map>
 #include <ostream>
 #include <sstream>
 #include <string>
@@ -29,7 +30,9 @@
 #include <simgear/nasal/cppbind/NasalHash.hxx>
 #include <simgear/nasal/naref.h>
 #include <simgear/props/props.hxx>
+#include <simgear/props/props_io.hxx>
 
+#include <Main/fg_props.hxx>
 #include <Main/globals.hxx>
 #include <Scripting/NasalSys.hxx>
 
@@ -266,6 +269,49 @@ int Addon::getLoadSequenceNumber() const
 void Addon::setLoadSequenceNumber(int num)
 { _loadSequenceNumber = num; }
 
+std::multimap<UrlType, QualifiedUrl> Addon::getUrls() const
+{
+  std::multimap<UrlType, QualifiedUrl> res;
+
+  auto appendIfNonEmpty = [&res](UrlType type, string url, string detail = "") {
+    if (!url.empty()) {
+      res.emplace(type, QualifiedUrl(type, std::move(url), std::move(detail)));
+    }
+  };
+
+  for (const auto& author: _authors) {
+    appendIfNonEmpty(UrlType::author, author->getUrl(), author->getName());
+  }
+
+  for (const auto& maint: _maintainers) {
+    appendIfNonEmpty(UrlType::maintainer, maint->getUrl(), maint->getName());
+  }
+
+  appendIfNonEmpty(UrlType::homePage, getHomePage());
+  appendIfNonEmpty(UrlType::download, getDownloadUrl());
+  appendIfNonEmpty(UrlType::support, getSupportUrl());
+  appendIfNonEmpty(UrlType::codeRepository, getCodeRepositoryUrl());
+  appendIfNonEmpty(UrlType::license, getLicenseUrl());
+
+  return res;
+}
+
+std::vector<SGPropertyNode_ptr> Addon::getMenubarNodes() const
+{ return _menubarNodes; }
+
+void Addon::setMenubarNodes(const std::vector<SGPropertyNode_ptr>& menubarNodes)
+{ _menubarNodes = menubarNodes; }
+
+void Addon::addToFGMenubar() const
+{
+  SGPropertyNode* menuRootNode = fgGetNode("/sim/menubar/default", true);
+
+  for (const auto& node: getMenubarNodes()) {
+    SGPropertyNode* childNode = menuRootNode->addChild("menu");
+    ::copyProperties(node.ptr(), childNode);
+  }
+}
+
 std::string Addon::str() const
 {
   std::ostringstream oss;
@@ -311,9 +357,81 @@ Addon Addon::fromAddonDir(const SGPath& addonPath)
   addon.setSupportUrl(std::move(metadata.supportUrl));
   addon.setCodeRepositoryUrl(std::move(metadata.codeRepositoryUrl));
 
+  SGPath menuFile = addonPath / "addon-menubar-items.xml";
+
+  if (menuFile.exists()) {
+    addon.setMenubarNodes(readMenubarItems(menuFile));
+  }
+
   return addon;
 }
 
+// Static method
+std::vector<SGPropertyNode_ptr>
+Addon::readMenubarItems(const SGPath& menuFile)
+{
+  SGPropertyNode rootNode;
+
+  try {
+    readProperties(menuFile, &rootNode);
+  } catch (const sg_exception &e) {
+    throw errors::error_loading_menubar_items_file(
+      "unable to load add-on menu bar items from file '" +
+      menuFile.utf8Str() + "': " + e.getFormattedMessage());
+  }
+
+  // Check the 'meta' section
+  SGPropertyNode *metaNode = rootNode.getChild("meta");
+  if (metaNode == nullptr) {
+    throw errors::error_loading_menubar_items_file(
+      "no /meta node found in add-on menu bar items file '" +
+      menuFile.utf8Str() + "'");
+  }
+
+  // Check the file type
+  SGPropertyNode *fileTypeNode = metaNode->getChild("file-type");
+  if (fileTypeNode == nullptr) {
+    throw errors::error_loading_menubar_items_file(
+      "no /meta/file-type node found in add-on menu bar items file '" +
+      menuFile.utf8Str() + "'");
+  }
+
+  string fileType = fileTypeNode->getStringValue();
+  if (fileType != "FlightGear add-on menu bar items") {
+    throw errors::error_loading_menubar_items_file(
+      "Invalid /meta/file-type value for add-on menu bar items file '" +
+      menuFile.utf8Str() + "': '" + fileType + "' "
+      "(expected 'FlightGear add-on menu bar items')");
+  }
+
+  // Check the format version
+  SGPropertyNode *fmtVersionNode = metaNode->getChild("format-version");
+  if (fmtVersionNode == nullptr) {
+    throw errors::error_loading_menubar_items_file(
+      "no /meta/format-version node found in add-on menu bar items file '" +
+      menuFile.utf8Str() + "'");
+  }
+
+  int formatVersion = fmtVersionNode->getIntValue();
+  if (formatVersion != 1) {
+    throw errors::error_loading_menubar_items_file(
+      "unknown format version in add-on menu bar items file '" +
+      menuFile.utf8Str() + "': " + std::to_string(formatVersion));
+  }
+
+  SG_LOG(SG_GENERAL, SG_DEBUG,
+         "Loaded add-on menu bar items from '" << menuFile.utf8Str() + "'");
+
+  SGPropertyNode *menubarItemsNode = rootNode.getChild("menubar-items");
+  std::vector<SGPropertyNode_ptr> res;
+
+  if (menubarItemsNode != nullptr) {
+    res = menubarItemsNode->getChildren("menu");
+  }
+
+  return res;
+}
+
 // Static method
 void Addon::setupGhost(nasal::Hash& addonsModule)
 {
diff --git a/src/Add-ons/Addon.hxx b/src/Add-ons/Addon.hxx
index 9cb3c5ad6..062216d43 100644
--- a/src/Add-ons/Addon.hxx
+++ b/src/Add-ons/Addon.hxx
@@ -173,6 +173,12 @@ public:
   // Get all non-empty URLs pertaining to this add-on
   std::multimap<UrlType, QualifiedUrl> getUrls() const;
 
+  // Getter and setter for the menu bar item nodes of the add-on
+  std::vector<SGPropertyNode_ptr> getMenubarNodes() const;
+  void setMenubarNodes(const std::vector<SGPropertyNode_ptr>& menubarNodes);
+  // Add the menus defined in addon-menubar-items.xml to /sim/menubar/default
+  void addToFGMenubar() const;
+
   // Simple string representation
   std::string str() const;
 
@@ -186,6 +192,10 @@ private:
   static SGPath getMetadataFile(const SGPath& addonPath);
   SGPath getMetadataFile() const;
 
+  // Read all menus from addon-menubar-items.xml (under the add-on base path)
+  static std::vector<SGPropertyNode_ptr>
+  readMenubarItems(const SGPath& menuFile);
+
   // The add-on identifier, in reverse DNS style. The AddonManager refuses to
   // register two add-ons with the same id in a given FlightGear session.
   std::string _id;
@@ -226,6 +236,8 @@ private:
   std::string _triggerProperty;
   // Semantics explained above
   int _loadSequenceNumber = -1;
+
+  std::vector<SGPropertyNode_ptr> _menubarNodes;
 };
 
 std::ostream& operator<<(std::ostream& os, const Addon& addon);
diff --git a/src/Add-ons/AddonManager.cxx b/src/Add-ons/AddonManager.cxx
index 74ab00e49..9faae1ca2 100644
--- a/src/Add-ons/AddonManager.cxx
+++ b/src/Add-ons/AddonManager.cxx
@@ -255,6 +255,14 @@ SGPropertyNode_ptr AddonManager::addonNode(const string& addonId) const
   return getAddon(addonId)->getAddonNode();
 }
 
+void
+AddonManager::addAddonMenusToFGMenubar() const
+{
+  for (const auto& addon: _registeredAddons) {
+    addon->addToFGMenubar();
+  }
+}
+
 } // of namespace addons
 
 } // of namespace flightgear
diff --git a/src/Add-ons/AddonManager.hxx b/src/Add-ons/AddonManager.hxx
index 942888b69..53a614c91 100644
--- a/src/Add-ons/AddonManager.hxx
+++ b/src/Add-ons/AddonManager.hxx
@@ -86,6 +86,10 @@ public:
   // Base node pertaining to the add-on in the Global Property Tree
   SGPropertyNode_ptr addonNode(const std::string& addonId) const;
 
+  // Add the 'menu' nodes defined by each registered add-on to
+  // /sim/menubar/default
+  void addAddonMenusToFGMenubar() const;
+
 private:
   // Constructor called from createInstance() only
   explicit AddonManager() = default;
diff --git a/src/Add-ons/addon_fwd.hxx b/src/Add-ons/addon_fwd.hxx
index 390953282..cb5ef9889 100644
--- a/src/Add-ons/addon_fwd.hxx
+++ b/src/Add-ons/addon_fwd.hxx
@@ -56,6 +56,7 @@ class error;
 class error_loading_config_file;
 class no_metadata_file_found;
 class error_loading_metadata_file;
+class error_loading_menubar_items_file;
 class duplicate_registration_attempt;
 class fg_version_too_old;
 class fg_version_too_recent;
diff --git a/src/Add-ons/exceptions.hxx b/src/Add-ons/exceptions.hxx
index 08ede87d6..0fb162cf1 100644
--- a/src/Add-ons/exceptions.hxx
+++ b/src/Add-ons/exceptions.hxx
@@ -50,6 +50,9 @@ class no_metadata_file_found : public error
 class error_loading_metadata_file : public error
 { using error::error; };
 
+class error_loading_menubar_items_file : public error
+{ using error::error; };
+
 class duplicate_registration_attempt : public error
 { using error::error; };
 
diff --git a/src/GUI/AddCatalogDialog.cxx b/src/GUI/AddCatalogDialog.cxx
index b7d91314c..a0bd19b0f 100644
--- a/src/GUI/AddCatalogDialog.cxx
+++ b/src/GUI/AddCatalogDialog.cxx
@@ -84,7 +84,12 @@ CatalogRef AddCatalogDialog::addedCatalog()
 void AddCatalogDialog::setNonInteractiveMode()
 {
     m_nonInteractiveMode = true;
-     ui->buttonBox->hide();
+    ui->buttonBox->hide();
+}
+
+void AddCatalogDialog::setUpdatingExistingCatalog()
+{
+    m_updatingExistingCatalog = true;
 }
 
 void AddCatalogDialog::setUrlAndDownload(QUrl url)
@@ -187,10 +192,23 @@ void AddCatalogDialog::accept()
 
 void AddCatalogDialog::reject()
 {
-    if (m_result && !m_result->id().empty()) {
-        // user may have successfully download the catalog, but choosen
-        // not to add it. so remove it here
-        m_packageRoot->removeCatalogById(m_result->id());
+    // user may have successfully download the catalog, but choosen
+    // not to add it. so remove it here
+
+    // however, if we got in here as part of re-validating an existing
+    // disabled catalog, *but* the re-validation also failed, we do not
+    // want to remove it here.
+
+    if (m_result && !m_result->id().empty())
+    {
+        if (m_updatingExistingCatalog) {
+            qWarning() << "cancelled add, but existing catalog so not removing:"
+                       << QString::fromStdString(m_result->id());
+        } else {
+            qWarning() << "removed cancelled catalog:"
+                          << QString::fromStdString(m_result->id());
+            m_packageRoot->removeCatalogById(m_result->id());
+        }
     }
 
     QDialog::reject();
diff --git a/src/GUI/AddCatalogDialog.hxx b/src/GUI/AddCatalogDialog.hxx
index fcea7313e..da5f2cda1 100644
--- a/src/GUI/AddCatalogDialog.hxx
+++ b/src/GUI/AddCatalogDialog.hxx
@@ -52,6 +52,13 @@ public:
      */
     void setNonInteractiveMode();
 
+    /**
+     * @brief setUpdatingExistingCatalog - indicate that this is an update or
+     * fix of an existing catalog, in which case we will treat failures /
+     * cancellation differently.
+     */
+    void setUpdatingExistingCatalog();
+
     void setUrlAndDownload(QUrl url);
 private slots:
     virtual void reject();
@@ -82,7 +89,7 @@ private:
     QUrl m_catalogUrl;
     simgear::pkg::CatalogRef m_result;
     bool m_nonInteractiveMode = false;
-
+    bool m_updatingExistingCatalog = false;
     std::unique_ptr<AddCatalogDelegate> m_delegate;
 };
 
diff --git a/src/GUI/AircraftModel.cxx b/src/GUI/AircraftModel.cxx
index 316d6fc75..241bd774f 100644
--- a/src/GUI/AircraftModel.cxx
+++ b/src/GUI/AircraftModel.cxx
@@ -67,6 +67,8 @@ protected:
             qWarning() << "failed refresh of "
                 << QString::fromStdString(aCatalog->url()) << ":" << aReason << endl;
         }
+
+        m_model->catalogsRefreshed();
     }
 
     void startInstall(InstallRef aInstall) override
diff --git a/src/GUI/AircraftModel.hxx b/src/GUI/AircraftModel.hxx
index 8cd85c246..84e03b781 100644
--- a/src/GUI/AircraftModel.hxx
+++ b/src/GUI/AircraftModel.hxx
@@ -121,6 +121,7 @@ signals:
     
     void aircraftNeedingUpdatedChanged();
 
+    void catalogsRefreshed();
 public slots:
     void setShowUpdateAll(bool showUpdateAll);
 
diff --git a/src/GUI/CatalogListModel.cxx b/src/GUI/CatalogListModel.cxx
index b60f22d28..4d0de86c3 100644
--- a/src/GUI/CatalogListModel.cxx
+++ b/src/GUI/CatalogListModel.cxx
@@ -33,10 +33,13 @@
 // FlightGear
 #include <Main/globals.hxx>
 
+using namespace simgear::pkg;
+
 CatalogListModel::CatalogListModel(QObject* pr, simgear::pkg::RootRef& rootRef) :
     QAbstractListModel(pr),
     m_packageRoot(rootRef)
 {
+    refresh();
 }
 
 CatalogListModel::~CatalogListModel()
@@ -46,21 +49,39 @@ CatalogListModel::~CatalogListModel()
 void CatalogListModel::refresh()
 {
     beginResetModel();
+    m_catalogs = m_packageRoot->allCatalogs();
     endResetModel();
 }
 
 int CatalogListModel::rowCount(const QModelIndex& parent) const
 {
-    return m_packageRoot->catalogs().size();
+    return m_catalogs.size();
 }
 
 QVariant CatalogListModel::data(const QModelIndex& index, int role) const
 {
-    simgear::pkg::CatalogRef cat = m_packageRoot->catalogs().at(index.row());
+    simgear::pkg::CatalogRef cat = m_catalogs.at(index.row());
 
     if (role == Qt::DisplayRole) {
         QString name = QString::fromStdString(cat->name());
-        QString desc = QString::fromStdString(cat->description()).simplified();
+        QString desc;
+        if (cat->isEnabled()) {
+            desc = QString::fromStdString(cat->description()).simplified();
+        } else {
+            switch (cat->status()) {
+            case Delegate::FAIL_NOT_FOUND:
+                desc = tr("The catalog data was not found on the server at the expected location (URL)");
+                break;
+            case Delegate::FAIL_VERSION:
+                desc =  tr("The catalog is not comaptible with the version of FlightGear");
+                break;
+            case Delegate::FAIL_HTTP_FORBIDDEN:
+                desc = tr("The catalog server is blocking access from some reason (forbidden)");
+                break;
+            default:
+                desc = tr("disabled due to an internal error");
+            }
+        }
         return tr("%1 - %2").arg(name).arg(desc);
     } else if (role == Qt::ToolTipRole) {
         return QString::fromStdString(cat->url());
@@ -81,3 +102,13 @@ bool CatalogListModel::setData(const QModelIndex &index, const QVariant &value,
 {
     return false;
 }
+
+Qt::ItemFlags CatalogListModel::flags(const QModelIndex &index) const
+{
+    Qt::ItemFlags r = Qt::ItemIsSelectable;
+    const auto cat = m_catalogs.at(index.row());
+    if (cat->isEnabled()) {
+        r |= Qt::ItemIsEnabled;
+    }
+    return r;
+}
diff --git a/src/GUI/CatalogListModel.hxx b/src/GUI/CatalogListModel.hxx
index 8b3fc4723..9df679f52 100644
--- a/src/GUI/CatalogListModel.hxx
+++ b/src/GUI/CatalogListModel.hxx
@@ -45,17 +45,20 @@ public:
 
     void refresh();
 
-    virtual int rowCount(const QModelIndex& parent) const;
+    int rowCount(const QModelIndex& parent) const override;
 
-    virtual QVariant data(const QModelIndex& index, int role) const;
+    QVariant data(const QModelIndex& index, int role) const override;
     
-    virtual bool setData(const QModelIndex &index, const QVariant &value, int role);
+    bool setData(const QModelIndex &index, const QVariant &value, int role) override;
+
+    Qt::ItemFlags flags(const QModelIndex &index) const override;
 
 private slots:
 
 
 private:
     simgear::pkg::RootRef m_packageRoot;
+    simgear::pkg::CatalogList m_catalogs;
 };
 
 #endif // of FG_GUI_CATALOG_LIST_MODEL
diff --git a/src/GUI/LauncherMainWindow.cxx b/src/GUI/LauncherMainWindow.cxx
index 7766fafe9..a18b44ff2 100644
--- a/src/GUI/LauncherMainWindow.cxx
+++ b/src/GUI/LauncherMainWindow.cxx
@@ -104,7 +104,6 @@ LauncherMainWindow::LauncherMainWindow() :
             this, &LauncherMainWindow::onViewCommandLine);
 
     m_serversModel = new MPServersModel(this);
-    m_serversModel->refresh();
 
     // keep the description QLabel in sync as the current item changes
     connect(m_ui->stateCombo,
@@ -151,7 +150,6 @@ LauncherMainWindow::LauncherMainWindow() :
     m_ui->locationHistory->setIcon(historyIcon);
 
     m_aircraftModel = new AircraftItemModel(this);
-
     m_installedAircraftModel = new AircraftProxyModel(this, m_aircraftModel);
     m_installedAircraftModel->setInstalledFilterEnabled(true);
 
@@ -185,6 +183,9 @@ LauncherMainWindow::LauncherMainWindow() :
             this, &LauncherMainWindow::onAircraftPathsChanged);
     m_ui->stack->addWidget(addOnsPage);
 
+    connect (m_aircraftModel, &AircraftItemModel::catalogsRefreshed,
+             addOnsPage, &AddOnsPage::onCatalogsRefreshed);
+
     QSettings settings;
     LocalAircraftCache::instance()->setPaths(settings.value("aircraft-paths").toStringList());
     LocalAircraftCache::instance()->scanDirs();
@@ -1015,6 +1016,11 @@ void LauncherMainWindow::requestUpdateAllAircraft()
     });
 }
 
+void LauncherMainWindow::queryMPServers()
+{
+    m_serversModel->refresh();
+}
+
 bool LauncherMainWindow::showNoOfficialHanger() const
 {
     return shouldShowOfficialCatalogMessage();
diff --git a/src/GUI/LauncherMainWindow.hxx b/src/GUI/LauncherMainWindow.hxx
index 3a43aef8b..d21ef850c 100644
--- a/src/GUI/LauncherMainWindow.hxx
+++ b/src/GUI/LauncherMainWindow.hxx
@@ -84,6 +84,8 @@ public:
 
     Q_INVOKABLE void requestUpdateAllAircraft();
 
+    Q_INVOKABLE void queryMPServers();
+
     bool showNoOfficialHanger() const;
 
     Q_INVOKABLE void officialCatalogAction(QString s);
diff --git a/src/GUI/MPSettings.qml b/src/GUI/MPSettings.qml
index 7c3c98a47..b9e6a68cc 100644
--- a/src/GUI/MPSettings.qml
+++ b/src/GUI/MPSettings.qml
@@ -13,6 +13,13 @@ Section {
             + "flight. This requires a moderately fast Internet connection to be usable. Your aircraft "
             + "will be visible to other users online, and you will see their aircraft.")
         keywords: ["network", "mp", "multiplay","online"]
+
+        onCheckedChanged: {
+            if (checked) {
+                // kick off a server query now
+                _launcher.queryMPServers();
+            }
+        }
     }
 
     LineEdit {
@@ -100,7 +107,12 @@ Section {
     }
 
     onRestore:  {
-        // nothing to do, restoration is done by the C++ code
+        if (enableMP.checked) {
+            // only query servers if MP is enabled
+            _launcher.queryMPServers();
+        }
+
+        // restoration is done by the C++ code
         // in MPServersModel::restoreMPServerSelection
     }
 
diff --git a/src/GUI/MapWidget.cxx b/src/GUI/MapWidget.cxx
index e28df0e21..f636e5441 100644
--- a/src/GUI/MapWidget.cxx
+++ b/src/GUI/MapWidget.cxx
@@ -787,7 +787,7 @@ void MapWidget::paintRuler()
   SGVec2d acftPos = project(_aircraft);
   SGVec2d clickPos = project(_clickGeod);
 
-  glColor4f(0.0, 1.0, 1.0, 0.6);
+  glColor3f(0.0, 1.0, 1.0);
   drawLine(acftPos, clickPos);
 
   circleAtAlt(clickPos, 8, 10, 5);
@@ -812,7 +812,7 @@ void MapWidget::paintAircraftLocation(const SGGeod& aircraftPos)
   double hdg = fgGetDouble("/orientation/heading-deg");
 
   glLineWidth(2.0);
-  glColor4f(1.0, 1.0, 0.0, 1.0);
+  glColor3f(1.0, 1.0, 0.0);
   glPushMatrix();
   glTranslated(loc.x(), loc.y(), 0.0);
   glRotatef(hdg - _upHeading, 0.0, 0.0, -1.0);
@@ -848,9 +848,9 @@ void MapWidget::paintRoute()
     }
 
     if (w < _route->currentIndex()) {
-      glColor4f(0.5, 0.5, 0.5, 0.7);
+      glColor3f(0.5, 0.5, 0.5);
     } else {
-      glColor4f(1.0, 0.0, 1.0, 1.0);
+      glColor3f(1.0, 0.0, 1.0);
     }
 
     flightgear::WayptRef wpt(_route->wayptAtIndex(w));
@@ -879,7 +879,7 @@ void MapWidget::paintRoute()
     }
 
     SGVec2d p = project(g);
-    glColor4f(1.0, 0.0, 1.0, 1.0);
+    glColor3f(1.0, 0.0, 1.0);
     circleAtAlt(p, 8, 12, 5);
 
     std::ostringstream legend;
@@ -912,7 +912,7 @@ void MapWidget::drawFlightHistory()
   // first pass, draw the actual lines
   glLineWidth(2.0);
   
-  glColor4f(0.0, 0.0, 1.0, 0.7);
+  glColor3f(0.0, 0.0, 1.0);
 
   glBegin(GL_LINE_STRIP);
   for (unsigned int i=0; i<_flightHistoryPath.size(); ++i) {
@@ -987,7 +987,7 @@ void MapWidget::drawLatLonGrid()
   int ix = 0;
   int iy = 0;
 
-  glColor4f(0.8, 0.8, 0.8, 1.0);
+  glColor3f(0.8, 0.8, 0.8);
   glBegin(GL_LINES);
   bool didDraw;
   do {
@@ -1038,7 +1038,7 @@ void MapWidget::drawGPSData()
     SGGeod trackRadial;
     SGGeodesy::direct(_aircraft, gpsTrackDeg, _drawRangeNm * SG_NM_TO_METER, trackRadial, az2);
 
-    glColor4f(1.0, 1.0, 0.0, 1.0);
+    glColor3f(1.0, 1.0, 0.0);
     glEnable(GL_LINE_STIPPLE);
     glLineStipple(1, 0x00FF);
     drawLine(project(_aircraft), project(trackRadial));
@@ -1049,7 +1049,7 @@ void MapWidget::drawGPSData()
     SGVec2d wp0Pos = project(wp0Geod);
     SGVec2d wp1Pos = project(wp1Geod);
 
-    glColor4f(1.0, 0.0, 1.0, 1.0);
+    glColor3f(1.0, 0.0, 1.0);
     drawLine(wp0Pos, wp1Pos);
 
   }
@@ -1387,7 +1387,7 @@ void MapWidget::drawRunwayPre(FGRunway* rwy)
 
   glLineWidth(4.0);
   glColor3f(1.0, 0.0, 1.0);
-	drawLine(p1, p2);
+  drawLine(p1, p2);
 }
 
 void MapWidget::drawRunway(FGRunway* rwy)
diff --git a/src/GUI/PathsDialog.cxx b/src/GUI/PathsDialog.cxx
index d19879ebc..940a5ea8a 100644
--- a/src/GUI/PathsDialog.cxx
+++ b/src/GUI/PathsDialog.cxx
@@ -27,7 +27,8 @@ AddOnsPage::AddOnsPage(QWidget *parent, simgear::pkg::RootRef root) :
     
     m_catalogsModel = new CatalogListModel(this, m_packageRoot);
     m_ui->catalogsList->setModel(m_catalogsModel);
-
+    connect(m_ui->catalogsList, &QListView::doubleClicked,
+            this, &AddOnsPage::onCatalogDoubleClicked);
  // enable drag-drop to re-order the paths
     m_ui->sceneryPathsList->setDragEnabled(true);
     m_ui->sceneryPathsList->setDragDropMode(QAbstractItemView::InternalMove);
@@ -245,7 +246,12 @@ void AddOnsPage::addDefaultCatalog(QWidget* pr, bool silent)
     }
     dlg->setUrlAndDownload(url);
     dlg->exec();
+}
 
+void AddOnsPage::onCatalogsRefreshed()
+{
+    m_catalogsModel->refresh();
+    updateUi();
 }
 
 void AddOnsPage::onRemoveCatalog()
@@ -280,6 +286,18 @@ void AddOnsPage::onRemoveCatalog()
     updateUi();
 }
 
+void AddOnsPage::onCatalogDoubleClicked(const QModelIndex& index)
+{
+    if ((index.flags() & Qt::ItemIsEnabled) == false) {
+        // re-validate existing catalog
+        QScopedPointer<AddCatalogDialog> dlg(new AddCatalogDialog(this, m_packageRoot));
+        dlg->setUpdatingExistingCatalog();
+        dlg->setUrlAndDownload(index.data(CatalogUrlRole).toUrl());
+        dlg->exec();
+        m_catalogsModel->refresh();
+    }
+}
+
 void AddOnsPage::onInstallScenery()
 {
     QSettings settings;
diff --git a/src/GUI/PathsDialog.hxx b/src/GUI/PathsDialog.hxx
index 1361d4ac8..896bf7c7d 100644
--- a/src/GUI/PathsDialog.hxx
+++ b/src/GUI/PathsDialog.hxx
@@ -22,6 +22,9 @@ public:
 
     static void addDefaultCatalog(QWidget* pr, bool silent);
     
+public slots:
+    void onCatalogsRefreshed();
+
 signals:
     void sceneryPathsChanged();
     void aircraftPathsChanged();
@@ -43,6 +46,8 @@ private slots:
 
     void saveAircraftPaths();
     void saveSceneryPaths();
+
+    void onCatalogDoubleClicked(const QModelIndex& index);
 private:
     void updateUi();
 
diff --git a/src/GUI/QmlAircraftInfo.cxx b/src/GUI/QmlAircraftInfo.cxx
index dd86c4305..c449204e0 100644
--- a/src/GUI/QmlAircraftInfo.cxx
+++ b/src/GUI/QmlAircraftInfo.cxx
@@ -318,7 +318,8 @@ QVariantList QmlAircraftInfo::previews() const
 {
     if (_item) {
         QVariantList result;
-        Q_FOREACH(QUrl u, _item->previews) {
+        auto actualItem = resolveItem();
+        Q_FOREACH(QUrl u, actualItem->previews) {
             result.append(u);
         }
         return result;
@@ -488,7 +489,9 @@ void QmlAircraftInfo::setUri(QUrl u)
         auto ident = u.path().toStdString();
         try {
             _package = globals->packageRoot()->getPackageById(ident);
-            _variant = _package->indexOfVariant(ident);
+            if (_package) {
+                _variant = _package->indexOfVariant(ident);
+            }
         } catch (sg_exception&) {
             qWarning() << "couldn't find package/variant for " << u;
         }
diff --git a/src/GUI/new_gui.cxx b/src/GUI/new_gui.cxx
index a2d6b3979..58cd8dfa2 100644
--- a/src/GUI/new_gui.cxx
+++ b/src/GUI/new_gui.cxx
@@ -21,6 +21,7 @@
 #include <boost/algorithm/string/case_conv.hpp>
 #include <boost/foreach.hpp>
 
+#include <Add-ons/AddonManager.hxx>
 #include <Main/fg_props.hxx>
 
 #if defined(SG_UNIX) && !defined(SG_MAC) 
@@ -82,7 +83,17 @@ NewGUI::init ()
     if (aircraftDialogDir.exists()) {
         readDir(aircraftDialogDir);
     }
-    
+
+    // Read XML dialogs made available by registered add-ons
+    const auto& addonManager = flightgear::addons::AddonManager::instance();
+    for (const auto& addon: addonManager->registeredAddons()) {
+        SGPath addonDialogDir = addon->getBasePath() / "gui/dialogs";
+
+        if (addonDialogDir.exists()) {
+            readDir(addonDialogDir);
+        }
+    }
+
     // Fix for http://code.google.com/p/flightgear-bugs/issues/detail?id=947
     fgGetNode("sim/menubar")->setAttribute(SGPropertyNode::PRESERVE, true);
     _menubar->init();
diff --git a/src/GUI/qml/AircraftCompactDelegate.qml b/src/GUI/qml/AircraftCompactDelegate.qml
index 503ceded7..afa61fe70 100644
--- a/src/GUI/qml/AircraftCompactDelegate.qml
+++ b/src/GUI/qml/AircraftCompactDelegate.qml
@@ -95,6 +95,7 @@ Item {
             width: parent.width
             text: root.__showAlternateText ? root.alternateText()
                                            : model.description
+            font.pixelSize: Style.baseFontPixelSize
             maximumLineCount: 3
             wrapMode: Text.WordWrap
             elide: Text.ElideRight
diff --git a/src/GUI/qml/AircraftDetailsView.qml b/src/GUI/qml/AircraftDetailsView.qml
index 2241ca9b8..3f85a1a24 100644
--- a/src/GUI/qml/AircraftDetailsView.qml
+++ b/src/GUI/qml/AircraftDetailsView.qml
@@ -100,7 +100,7 @@ Rectangle {
                             width: parent.width
                             wrapMode: Text.WordWrap
                             visible: aircraft.description != ""
-                            font.pixelSize: 14
+                            font.pixelSize: Style.baseFontPixelSize
                         }
 
                         Text {
@@ -110,7 +110,7 @@ Rectangle {
                             anchors.horizontalCenter: parent.horizontalCenter
                             wrapMode: Text.WordWrap
                             visible: (aircraft.authors != undefined)
-
+                            font.pixelSize: Style.baseFontPixelSize
                         }
                     }
 
@@ -146,6 +146,7 @@ Rectangle {
                     Text {
                         id: ratingsLabel
                         text: qsTr("Ratings:")
+                        font.pixelSize: Style.baseFontPixelSize
                     }
 
 
@@ -192,6 +193,7 @@ Rectangle {
                     width: parent.width
                     wrapMode: Text.WrapAtWordBoundaryOrAnywhere
                     visible: aircraft.pathOnDisk != undefined
+                    font.pixelSize: Style.baseFontPixelSize
                 }
 
             } // main layout column
diff --git a/src/GUI/qml/AircraftDownloadPanel.qml b/src/GUI/qml/AircraftDownloadPanel.qml
index 54dc49300..e488b9c5a 100644
--- a/src/GUI/qml/AircraftDownloadPanel.qml
+++ b/src/GUI/qml/AircraftDownloadPanel.qml
@@ -1,5 +1,6 @@
 import QtQuick 2.0
 import FlightGear.Launcher 1.0
+import "." // -> forces the qmldir to be loaded
 
 Item {
     id: root
@@ -143,6 +144,7 @@ Item {
         anchors.leftMargin: 6
         anchors.verticalCenter: button.verticalCenter
         text: "Size: " + (root.packageSize / 0x100000).toFixed(1) + "MB"
+        font.pixelSize: Style.baseFontPixelSize
     }
 
     Column {
@@ -185,6 +187,7 @@ Item {
             visible: false
             text: (compact ? "" : "Downloaded ") + (root.downloadedBytes / 0x100000).toFixed(1) +
                   "MB of " + (root.packageSize / 0x100000).toFixed(1) + "MB";
+            font.pixelSize: Style.baseFontPixelSize
         }
     } // item container for progress bar and text
 }
diff --git a/src/GUI/qml/AircraftRating.qml b/src/GUI/qml/AircraftRating.qml
index e04487d68..08ec59d68 100644
--- a/src/GUI/qml/AircraftRating.qml
+++ b/src/GUI/qml/AircraftRating.qml
@@ -18,6 +18,7 @@ Item {
 
         horizontalAlignment: Text.AlignRight
         text: root.title + ":"
+        font.pixelSize: Style.baseFontPixelSize
     }
 
     Row {
diff --git a/src/GUI/qml/AircraftVariantChoice.qml b/src/GUI/qml/AircraftVariantChoice.qml
index 5ad5f4e08..9a11453cc 100644
--- a/src/GUI/qml/AircraftVariantChoice.qml
+++ b/src/GUI/qml/AircraftVariantChoice.qml
@@ -1,5 +1,6 @@
 import QtQuick 2.0
 import QtQuick.Window 2.0
+import "." // -> forces the qmldir to be loaded
 
 import FlightGear.Launcher 1.0
 
@@ -37,8 +38,9 @@ Rectangle {
         anchors.rightMargin: 4
 
         horizontalAlignment: Text.AlignHCenter
-        font.pixelSize: 24
+        font.pixelSize: Style.baseFontPixelSize * 2
         text: aircraftInfo.name
+        fontSizeMode: Text.Fit
 
         elide: Text.ElideRight
         maximumLineCount: 1
diff --git a/src/GUI/qml/Button.qml b/src/GUI/qml/Button.qml
index 4733c7434..97679b75a 100644
--- a/src/GUI/qml/Button.qml
+++ b/src/GUI/qml/Button.qml
@@ -20,6 +20,7 @@ Rectangle {
         anchors.centerIn: parent
         color: "white"
         text: (mouse.containsMouse && hoverText != "") ? root.hoverText : root.text
+        font.pixelSize: Style.baseFontPixelSize
     }
 
     MouseArea {
diff --git a/src/GUI/qml/Slider.qml b/src/GUI/qml/Slider.qml
index 9bfd3f4b1..901f37f74 100644
--- a/src/GUI/qml/Slider.qml
+++ b/src/GUI/qml/Slider.qml
@@ -20,6 +20,7 @@ Item {
         id: labelText
         width: parent.width - (emptyTrack.width + Style.margin)
         horizontalAlignment: Text.AlignRight
+        font.pixelSize: Style.baseFontPixelSize
     }
 
     Rectangle {
diff --git a/src/GUI/qml/Style.qml b/src/GUI/qml/Style.qml
index 26f117031..05f075d2d 100644
--- a/src/GUI/qml/Style.qml
+++ b/src/GUI/qml/Style.qml
@@ -18,5 +18,7 @@ QtObject
     readonly property string inactiveThemeColor: "#9f9f9f"
 
     readonly property string baseTextColor: "#3f3f3f"
+
+    readonly property int baseFontPixelSize: 12
 }
 
diff --git a/src/GUI/qml/ToggleSwitch.qml b/src/GUI/qml/ToggleSwitch.qml
index e47ff317a..2eb45c43b 100644
--- a/src/GUI/qml/ToggleSwitch.qml
+++ b/src/GUI/qml/ToggleSwitch.qml
@@ -45,6 +45,7 @@ Item {
         anchors.left: track.right
         anchors.leftMargin: Style.margin
         anchors.verticalCenter: parent.verticalCenter
+        font.pixelSize: Style.baseFontPixelSize
     }
 
     MouseArea {
diff --git a/src/Main/main.cxx b/src/Main/main.cxx
index 74a61afc6..40578b8d4 100644
--- a/src/Main/main.cxx
+++ b/src/Main/main.cxx
@@ -585,6 +585,9 @@ int fgMainInit( int argc, char **argv )
     SG_LOG(SG_GENERAL, SG_INFO,
            "EmbeddedResourceManager: selected locale '" << locale << "'");
 
+    // Copy the property nodes for the menus added by registered add-ons
+    addons::AddonManager::instance()->addAddonMenusToFGMenubar();
+
     // Initialize the Window/Graphics environment.
     fgOSInit(&argc, argv);
     _bootstrap_OSInit++;
diff --git a/src/Network/HTTPClient.cxx b/src/Network/HTTPClient.cxx
index af0f19a76..d152a95cb 100644
--- a/src/Network/HTTPClient.cxx
+++ b/src/Network/HTTPClient.cxx
@@ -238,8 +238,9 @@ void FGHTTPClient::postinit()
   .method("refresh", &pkg::Catalog::refresh)
   .method("needingUpdate", &pkg::Catalog::packagesNeedingUpdate)
   .member("installed", &pkg::Catalog::installedPackages)
-  .method("search", &f_catalog_search);
-  
+  .method("search", &f_catalog_search)
+  .member("enabled", &pkg::Catalog::isEnabled);
+
   NasalPackage::init("Package")
   .member("id", &pkg::Package::id)
   .member("name", &pkg::Package::name)