diff --git a/web/pdf_sidebar.js b/web/pdf_sidebar.js
new file mode 100644
index 000000000..0490ef249
--- /dev/null
+++ b/web/pdf_sidebar.js
@@ -0,0 +1,324 @@
+/* Copyright 2016 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+ /* globals RenderingStates */
+
+'use strict';
+
+var SidebarView = {
+  NONE: 0,
+  THUMBS: 1,
+  OUTLINE: 2,
+  ATTACHMENTS: 3
+};
+
+/**
+ * @typedef {Object} PDFSidebarOptions
+ * @property {PDFViewer} - The document viewer.
+ * @property {PDFThumbnailViewer} - The thumbnail viewer.
+ * @property {PDFOutlineViewer} - The outline viewer.
+ * @property {HTMLDivElement} mainContainer - The main container
+ *   (in which the viewer element is placed).
+ * @property {HTMLDivElement} outerContainer - The outer container
+ *   (encasing both the viewer and sidebar elements).
+ * @property {HTMLButtonElement} toggleButton - The button used for
+ *   opening/closing the sidebar.
+ * @property {HTMLButtonElement} thumbnailButton - The button used to show
+ *   the thumbnail view.
+ * @property {HTMLButtonElement} outlineButton - The button used to show
+ *   the outline view.
+ * @property {HTMLButtonElement} attachmentsButton - The button used to show
+ *   the attachments view.
+ * @property {HTMLDivElement} thumbnailView - The container in which
+ *   the thumbnails are placed.
+ * @property {HTMLDivElement} outlineView - The container in which
+ *   the outline is placed.
+ * @property {HTMLDivElement} attachmentsView - The container in which
+ *   the attachments are placed.
+ */
+
+/**
+ * @class
+ */
+var PDFSidebar = (function PDFSidebarClosure() {
+  /**
+   * @constructs PDFSidebar
+   * @param {PDFSidebarOptions} options
+   */
+  function PDFSidebar(options) {
+    this.isOpen = false;
+    this.active = SidebarView.THUMBS;
+    this.isInitialViewSet = false;
+
+    /**
+     * Callback used when the sidebar has been opened/closed, to ensure that
+     * the viewers (PDFViewer/PDFThumbnailViewer) are updated correctly.
+     */
+    this.onToggled = null;
+
+    this.pdfViewer = options.pdfViewer;
+    this.pdfThumbnailViewer = options.pdfThumbnailViewer;
+    this.pdfOutlineViewer = options.pdfOutlineViewer;
+
+    this.mainContainer = options.mainContainer;
+    this.outerContainer = options.outerContainer;
+    this.toggleButton = options.toggleButton;
+
+    this.thumbnailButton = options.thumbnailButton;
+    this.outlineButton = options.outlineButton;
+    this.attachmentsButton = options.attachmentsButton;
+
+    this.thumbnailView = options.thumbnailView;
+    this.outlineView = options.outlineView;
+    this.attachmentsView = options.attachmentsView;
+
+    this._addEventListeners();
+  }
+
+  PDFSidebar.prototype = {
+    reset: function PDFSidebar_reset() {
+      this.isInitialViewSet = false;
+
+      this.close();
+      this.switchView(SidebarView.THUMBS);
+
+      this.outlineButton.disabled = false;
+      this.attachmentsButton.disabled = false;
+    },
+
+    /**
+     * @returns {number} One of the values in {SidebarView}.
+     */
+    get visibleView() {
+      return (this.isOpen ? this.active : SidebarView.NONE);
+    },
+
+    get isThumbnailViewVisible() {
+      return (this.isOpen && this.active === SidebarView.THUMBS);
+    },
+
+    get isOutlineViewVisible() {
+      return (this.isOpen && this.active === SidebarView.OUTLINE);
+    },
+
+    get isAttachmentsViewVisible() {
+      return (this.isOpen && this.active === SidebarView.ATTACHMENTS);
+    },
+
+    /**
+     * @param {number} view - The sidebar view that should become visible,
+     *                        must be one of the values in {SidebarView}.
+     */
+    setInitialView: function PDFSidebar_setInitialView(view) {
+      if (this.isInitialViewSet) {
+        return;
+      }
+      this.isInitialViewSet = true;
+
+      if (this.isOpen && view === SidebarView.NONE) {
+        // If the user has already manually opened the sidebar,
+        // immediately closing it would be bad UX.
+        return;
+      }
+      this.switchView(view, true);
+    },
+
+    /**
+     * @param {number} view - The sidebar view that should be switched to,
+     *                        must be one of the values in {SidebarView}.
+     * @param {boolean} forceOpen - Ensure that the sidebar is opened.
+     *                              The default value is false.
+     */
+    switchView: function PDFSidebar_switchView(view, forceOpen) {
+      if (view === SidebarView.NONE) {
+        this.close();
+        return;
+      }
+      if (forceOpen) {
+        this.open();
+      }
+      var shouldForceRendering = false;
+
+      switch (view) {
+        case SidebarView.THUMBS:
+          this.thumbnailButton.classList.add('toggled');
+          this.outlineButton.classList.remove('toggled');
+          this.attachmentsButton.classList.remove('toggled');
+
+          this.thumbnailView.classList.remove('hidden');
+          this.outlineView.classList.add('hidden');
+          this.attachmentsView.classList.add('hidden');
+
+          if (this.isOpen && view !== this.active) {
+            this._updateThumbnailViewer();
+            shouldForceRendering = true;
+          }
+          break;
+        case SidebarView.OUTLINE:
+          if (this.outlineButton.disabled) {
+            return;
+          }
+          this.thumbnailButton.classList.remove('toggled');
+          this.outlineButton.classList.add('toggled');
+          this.attachmentsButton.classList.remove('toggled');
+
+          this.thumbnailView.classList.add('hidden');
+          this.outlineView.classList.remove('hidden');
+          this.attachmentsView.classList.add('hidden');
+          break;
+        case SidebarView.ATTACHMENTS:
+          if (this.attachmentsButton.disabled) {
+            return;
+          }
+          this.thumbnailButton.classList.remove('toggled');
+          this.outlineButton.classList.remove('toggled');
+          this.attachmentsButton.classList.add('toggled');
+
+          this.thumbnailView.classList.add('hidden');
+          this.outlineView.classList.add('hidden');
+          this.attachmentsView.classList.remove('hidden');
+          break;
+        default:
+          console.error('PDFSidebar_switchView: "' + view +
+                        '" is an unsupported value.');
+          return;
+      }
+      // Update the active view *after* it has been validated above,
+      // in order to prevent setting it to an invalid state.
+      this.active = view | 0;
+
+      if (shouldForceRendering) {
+        this._forceRendering();
+      }
+    },
+
+    open: function PDFSidebar_open() {
+      if (this.isOpen) {
+        return;
+      }
+      this.isOpen = true;
+      this.toggleButton.classList.add('toggled');
+
+      this.outerContainer.classList.add('sidebarMoving');
+      this.outerContainer.classList.add('sidebarOpen');
+
+      if (this.active === SidebarView.THUMBS) {
+        this._updateThumbnailViewer();
+      }
+      this._forceRendering();
+    },
+
+    close: function PDFSidebar_close() {
+      if (!this.isOpen) {
+        return;
+      }
+      this.isOpen = false;
+      this.toggleButton.classList.remove('toggled');
+
+      this.outerContainer.classList.add('sidebarMoving');
+      this.outerContainer.classList.remove('sidebarOpen');
+
+      this._forceRendering();
+    },
+
+    toggle: function PDFSidebar_toggle() {
+      if (this.isOpen) {
+        this.close();
+      } else {
+        this.open();
+      }
+    },
+
+    /**
+     * @private
+     */
+    _forceRendering: function PDFSidebar_forceRendering() {
+      if (this.onToggled) {
+        this.onToggled();
+      } else { // Fallback
+        this.pdfViewer.forceRendering();
+        this.pdfThumbnailViewer.forceRendering();
+      }
+    },
+
+    /**
+     * @private
+     */
+    _updateThumbnailViewer: function PDFSidebar_updateThumbnailViewer() {
+      var pdfViewer = this.pdfViewer;
+      var thumbnailViewer = this.pdfThumbnailViewer;
+
+      // Use the rendered pages to set the corresponding thumbnail images.
+      var pagesCount = pdfViewer.pagesCount;
+      for (var pageIndex = 0; pageIndex < pagesCount; pageIndex++) {
+        var pageView = pdfViewer.getPageView(pageIndex);
+        if (pageView && pageView.renderingState === RenderingStates.FINISHED) {
+          var thumbnailView = thumbnailViewer.getThumbnail(pageIndex);
+          thumbnailView.setImage(pageView);
+        }
+      }
+      thumbnailViewer.scrollThumbnailIntoView(pdfViewer.currentPageNumber);
+    },
+
+    /**
+     * @private
+     */
+    _addEventListeners: function PDFSidebar_addEventListeners() {
+      var self = this;
+
+      self.mainContainer.addEventListener('transitionend', function(evt) {
+        if (evt.target === /* mainContainer */ this) {
+          self.outerContainer.classList.remove('sidebarMoving');
+        }
+      });
+
+      // Buttons for switching views.
+      self.thumbnailButton.addEventListener('click', function() {
+        self.switchView(SidebarView.THUMBS);
+      });
+
+      self.outlineButton.addEventListener('click', function() {
+        self.switchView(SidebarView.OUTLINE);
+      });
+      self.outlineButton.addEventListener('dblclick', function() {
+        self.pdfOutlineViewer.toggleOutlineTree();
+      });
+
+      self.attachmentsButton.addEventListener('click', function() {
+        self.switchView(SidebarView.ATTACHMENTS);
+      });
+
+      // Disable/enable views.
+      self.outlineView.addEventListener('outlineloaded', function(evt) {
+        var outlineCount = evt.detail.outlineCount;
+
+        self.outlineButton.disabled = !outlineCount;
+        if (!outlineCount && self.active === SidebarView.OUTLINE) {
+          self.switchView(SidebarView.THUMBS);
+        }
+      });
+
+      self.attachmentsView.addEventListener('attachmentsloaded', function(evt) {
+        var attachmentsCount = evt.detail.attachmentsCount;
+
+        self.attachmentsButton.disabled = !attachmentsCount;
+        if (!attachmentsCount && self.active === SidebarView.ATTACHMENTS) {
+          self.switchView(SidebarView.THUMBS);
+        }
+      });
+    },
+  };
+
+  return PDFSidebar;
+})();
diff --git a/web/preferences.js b/web/preferences.js
index e62b10d21..f0cd46f89 100644
--- a/web/preferences.js
+++ b/web/preferences.js
@@ -18,13 +18,6 @@
 
 //#include default_preferences.js
 
-var SidebarView = {
-  NONE: 0,
-  THUMBS: 1,
-  OUTLINE: 2,
-  ATTACHMENTS: 3
-};
-
 /**
  * Preferences - Utility for storing persistent settings.
  *   Used for settings that should be applied to all opened documents,
diff --git a/web/viewer.html b/web/viewer.html
index 9a366e13e..98ee82954 100644
--- a/web/viewer.html
+++ b/web/viewer.html
@@ -74,6 +74,7 @@ See https://github.com/adobe-type-tools/cmap-resources
     <script src="pdf_viewer.js"></script>
     <script src="pdf_thumbnail_view.js"></script>
     <script src="pdf_thumbnail_viewer.js"></script>
+    <script src="pdf_sidebar.js"></script>
     <script src="pdf_outline_viewer.js"></script>
     <script src="pdf_attachment_viewer.js"></script>
     <script src="pdf_find_bar.js"></script>
diff --git a/web/viewer.js b/web/viewer.js
index 506725214..1ab9ca30f 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -15,7 +15,7 @@
 /* globals PDFJS, PDFBug, FirefoxCom, Stats, ProgressBar, DownloadManager,
            getPDFFileNameFromURL, PDFHistory, Preferences, SidebarView,
            ViewHistory, Stats, PDFThumbnailViewer, URL, noContextMenuHandler,
-           SecondaryToolbar, PasswordPrompt, PDFPresentationMode,
+           SecondaryToolbar, PasswordPrompt, PDFPresentationMode, PDFSidebar,
            PDFDocumentProperties, HandTool, Promise, PDFLinkService,
            PDFOutlineViewer, PDFAttachmentViewer, OverlayManager,
            PDFFindController, PDFFindBar, PDFViewer, PDFRenderingQueue,
@@ -83,6 +83,7 @@ var mozL10n = document.mozL10n || document.webL10n;
 //#include pdf_document_properties.js
 //#include pdf_viewer.js
 //#include pdf_thumbnail_viewer.js
+//#include pdf_sidebar.js
 //#include pdf_outline_viewer.js
 //#include pdf_attachment_viewer.js
 
@@ -93,7 +94,6 @@ var PDFViewerApplication = {
   fellback: false,
   pdfDocument: null,
   pdfLoadingTask: null,
-  sidebarOpen: false,
   printing: false,
   /** @type {PDFViewer} */
   pdfViewer: null,
@@ -109,6 +109,8 @@ var PDFViewerApplication = {
   pdfLinkService: null,
   /** @type {PDFHistory} */
   pdfHistory: null,
+  /** @type {PDFSidebar} */
+  pdfSidebar: null,
   /** @type {PDFOutlineViewer} */
   pdfOutlineViewer: null,
   /** @type {PDFAttachmentViewer} */
@@ -259,6 +261,25 @@ var PDFViewerApplication = {
       downloadManager: new DownloadManager(),
     });
 
+    this.pdfSidebar = new PDFSidebar({
+      pdfViewer: this.pdfViewer,
+      pdfThumbnailViewer: this.pdfThumbnailViewer,
+      pdfOutlineViewer: this.pdfOutlineViewer,
+      // Divs (and sidebar button)
+      mainContainer: document.getElementById('mainContainer'),
+      outerContainer: document.getElementById('outerContainer'),
+      toggleButton: document.getElementById('sidebarToggle'),
+      // Buttons
+      thumbnailButton: document.getElementById('viewThumbnail'),
+      outlineButton: document.getElementById('viewOutline'),
+      attachmentsButton: document.getElementById('viewAttachments'),
+      // Views
+      thumbnailView: document.getElementById('thumbnailView'),
+      outlineView: document.getElementById('outlineView'),
+      attachmentsView: document.getElementById('attachmentsView'),
+    });
+    this.pdfSidebar.onToggled = this.forceRendering.bind(this);
+
     var self = this;
     var initializedPromise = Promise.all([
       Preferences.get('enableWebGL').then(function resolved(value) {
@@ -540,6 +561,7 @@ var PDFViewerApplication = {
       this.pdfLinkService.setDocument(null, null);
     }
 
+    this.pdfSidebar.reset();
     this.pdfOutlineViewer.reset();
     this.pdfAttachmentViewer.reset();
 
@@ -968,40 +990,12 @@ var PDFViewerApplication = {
     Promise.all(promises).then(function() {
       pdfDocument.getOutline().then(function(outline) {
         self.pdfOutlineViewer.render({ outline: outline });
-
-        var container = document.getElementById('outlineView');
-        document.getElementById('viewOutline').disabled = !outline;
-
-        if (!outline && !container.classList.contains('hidden')) {
-          self.switchSidebarView('thumbs');
-        }
-        if (outline &&
-            self.preferenceSidebarViewOnLoad === SidebarView.OUTLINE) {
-          self.switchSidebarView('outline', true);
-        }
       });
       pdfDocument.getAttachments().then(function(attachments) {
         self.pdfAttachmentViewer.render({ attachments: attachments });
-
-        var container = document.getElementById('attachmentsView');
-        document.getElementById('viewAttachments').disabled = !attachments;
-
-        if (!attachments && !container.classList.contains('hidden')) {
-          self.switchSidebarView('thumbs');
-        }
-        if (attachments &&
-            self.preferenceSidebarViewOnLoad === SidebarView.ATTACHMENTS) {
-          self.switchSidebarView('attachments', true);
-        }
       });
     });
 
-    if (self.preferenceSidebarViewOnLoad === SidebarView.THUMBS) {
-      Promise.all([firstPagePromise, onePageRendered]).then(function () {
-        self.switchSidebarView('thumbs', true);
-      });
-    }
-
     pdfDocument.getMetadata().then(function(data) {
       var info = data.info, metadata = data.metadata;
       self.documentInfo = info;
@@ -1080,6 +1074,8 @@ var PDFViewerApplication = {
     document.getElementById('pageNumber').value =
       this.pdfViewer.currentPageNumber;
 
+    this.pdfSidebar.setInitialView(this.preferenceSidebarViewOnLoad);
+
     if (this.initialDestination) {
       this.pdfLinkService.navigateTo(this.initialDestination);
       this.initialDestination = null;
@@ -1112,83 +1108,11 @@ var PDFViewerApplication = {
 
   forceRendering: function pdfViewForceRendering() {
     this.pdfRenderingQueue.printing = this.printing;
-    this.pdfRenderingQueue.isThumbnailViewEnabled = this.sidebarOpen;
+    this.pdfRenderingQueue.isThumbnailViewEnabled =
+      this.pdfSidebar.isThumbnailViewVisible;
     this.pdfRenderingQueue.renderHighestPriority();
   },
 
-  refreshThumbnailViewer: function pdfViewRefreshThumbnailViewer() {
-    var pdfViewer = this.pdfViewer;
-    var thumbnailViewer = this.pdfThumbnailViewer;
-
-    // set thumbnail images of rendered pages
-    var pagesCount = pdfViewer.pagesCount;
-    for (var pageIndex = 0; pageIndex < pagesCount; pageIndex++) {
-      var pageView = pdfViewer.getPageView(pageIndex);
-      if (pageView && pageView.renderingState === RenderingStates.FINISHED) {
-        var thumbnailView = thumbnailViewer.getThumbnail(pageIndex);
-        thumbnailView.setImage(pageView);
-      }
-    }
-
-    thumbnailViewer.scrollThumbnailIntoView(this.page);
-  },
-
-  switchSidebarView: function pdfViewSwitchSidebarView(view, openSidebar) {
-    if (openSidebar && !this.sidebarOpen) {
-      document.getElementById('sidebarToggle').click();
-    }
-    var thumbsView = document.getElementById('thumbnailView');
-    var outlineView = document.getElementById('outlineView');
-    var attachmentsView = document.getElementById('attachmentsView');
-
-    var thumbsButton = document.getElementById('viewThumbnail');
-    var outlineButton = document.getElementById('viewOutline');
-    var attachmentsButton = document.getElementById('viewAttachments');
-
-    switch (view) {
-      case 'thumbs':
-        var wasAnotherViewVisible = thumbsView.classList.contains('hidden');
-
-        thumbsButton.classList.add('toggled');
-        outlineButton.classList.remove('toggled');
-        attachmentsButton.classList.remove('toggled');
-        thumbsView.classList.remove('hidden');
-        outlineView.classList.add('hidden');
-        attachmentsView.classList.add('hidden');
-
-        this.forceRendering();
-
-        if (wasAnotherViewVisible) {
-          this.pdfThumbnailViewer.ensureThumbnailVisible(this.page);
-        }
-        break;
-
-      case 'outline':
-        if (outlineButton.disabled) {
-          return;
-        }
-        thumbsButton.classList.remove('toggled');
-        outlineButton.classList.add('toggled');
-        attachmentsButton.classList.remove('toggled');
-        thumbsView.classList.add('hidden');
-        outlineView.classList.remove('hidden');
-        attachmentsView.classList.add('hidden');
-        break;
-
-      case 'attachments':
-        if (attachmentsButton.disabled) {
-          return;
-        }
-        thumbsButton.classList.remove('toggled');
-        outlineButton.classList.remove('toggled');
-        attachmentsButton.classList.add('toggled');
-        thumbsView.classList.add('hidden');
-        outlineView.classList.add('hidden');
-        attachmentsView.classList.remove('hidden');
-        break;
-    }
-  },
-
   beforePrint: function pdfViewSetupBeforePrint() {
     if (!this.supportsPrinting) {
       var printMessage = mozL10n.get('printing_not_supported', null,
@@ -1527,48 +1451,18 @@ function webViewerInitialized() {
   // Suppress context menus for some controls
   document.getElementById('scaleSelect').oncontextmenu = noContextMenuHandler;
 
-  var mainContainer = document.getElementById('mainContainer');
-  var outerContainer = document.getElementById('outerContainer');
-  mainContainer.addEventListener('transitionend', function(e) {
-    if (e.target === mainContainer) {
-      var event = document.createEvent('UIEvents');
-      event.initUIEvent('resize', false, false, window, 0);
-      window.dispatchEvent(event);
-      outerContainer.classList.remove('sidebarMoving');
-    }
-  }, true);
+  document.getElementById('mainContainer').addEventListener('transitionend',
+    function(e) {
+      if (e.target === /* mainContainer */ this) {
+        var event = document.createEvent('UIEvents');
+        event.initUIEvent('resize', false, false, window, 0);
+        window.dispatchEvent(event);
+      }
+    }, true);
 
   document.getElementById('sidebarToggle').addEventListener('click',
     function() {
-      this.classList.toggle('toggled');
-      outerContainer.classList.add('sidebarMoving');
-      outerContainer.classList.toggle('sidebarOpen');
-      PDFViewerApplication.sidebarOpen =
-        outerContainer.classList.contains('sidebarOpen');
-      if (PDFViewerApplication.sidebarOpen) {
-        PDFViewerApplication.refreshThumbnailViewer();
-      }
-      PDFViewerApplication.forceRendering();
-    });
-
-  document.getElementById('viewThumbnail').addEventListener('click',
-    function() {
-      PDFViewerApplication.switchSidebarView('thumbs');
-    });
-
-  document.getElementById('viewOutline').addEventListener('click',
-    function() {
-      PDFViewerApplication.switchSidebarView('outline');
-    });
-
-  document.getElementById('viewOutline').addEventListener('dblclick',
-    function() {
-      PDFViewerApplication.pdfOutlineViewer.toggleOutlineTree();
-    });
-
-  document.getElementById('viewAttachments').addEventListener('click',
-    function() {
-      PDFViewerApplication.switchSidebarView('attachments');
+      PDFViewerApplication.pdfSidebar.toggle();
     });
 
   document.getElementById('previous').addEventListener('click',
@@ -1668,7 +1562,8 @@ document.addEventListener('pagerendered', function (e) {
   var pageIndex = pageNumber - 1;
   var pageView = PDFViewerApplication.pdfViewer.getPageView(pageIndex);
 
-  if (PDFViewerApplication.sidebarOpen) {
+  // Use the rendered page to set the corresponding thumbnail image.
+  if (PDFViewerApplication.pdfSidebar.isThumbnailViewVisible) {
     var thumbnailView = PDFViewerApplication.pdfThumbnailViewer.
                         getThumbnail(pageIndex);
     thumbnailView.setImage(pageView);
@@ -1736,23 +1631,26 @@ document.addEventListener('pagemode', function (evt) {
     return;
   }
   // Handle the 'pagemode' hash parameter, see also `PDFLinkService_setHash`.
-  var mode = evt.detail.mode;
+  var mode = evt.detail.mode, view;
   switch (mode) {
-    case 'bookmarks':
-      // Note: Our code calls this property 'outline', even though the
-      //       Open Parameter specification calls it 'bookmarks'.
-      mode = 'outline';
-      /* falls through */
     case 'thumbs':
+      view = SidebarView.THUMBS;
+      break;
+    case 'bookmarks':
+    case 'outline':
+      view = SidebarView.OUTLINE;
+      break;
     case 'attachments':
-      PDFViewerApplication.switchSidebarView(mode, true);
+      view = SidebarView.ATTACHMENTS;
       break;
     case 'none':
-      if (PDFViewerApplication.sidebarOpen) {
-        document.getElementById('sidebarToggle').click();
-      }
+      view = SidebarView.NONE;
       break;
+    default:
+      console.error('Invalid "pagemode" hash parameter: ' + mode);
+      return;
   }
+  PDFViewerApplication.pdfSidebar.switchView(view, /* forceOpen = */ true);
 }, true);
 
 document.addEventListener('namedaction', function (e) {
@@ -1954,7 +1852,8 @@ window.addEventListener('pagechange', function pagechange(evt) {
   var page = evt.pageNumber;
   if (evt.previousPageNumber !== page) {
     document.getElementById('pageNumber').value = page;
-    if (PDFViewerApplication.sidebarOpen) {
+
+    if (PDFViewerApplication.pdfSidebar.isThumbnailViewVisible) {
       PDFViewerApplication.pdfThumbnailViewer.scrollThumbnailIntoView(page);
     }
   }