diff --git a/extensions/chromium/options/migration.js b/extensions/chromium/options/migration.js
index ca547850c4214..d2d8720d4eb9c 100644
--- a/extensions/chromium/options/migration.js
+++ b/extensions/chromium/options/migration.js
@@ -81,6 +81,9 @@ limitations under the License.
       'disableTextLayer',
       'enhanceTextSelection',
       'textLayerMode',
+      'showPreviousViewOnLoad',
+      'disablePageMode',
+      'viewOnLoad',
     ], function(items) {
       // Migration code for https://github.com/mozilla/pdf.js/pull/7635.
       if (typeof items.enableHandToolOnLoad === 'boolean') {
@@ -113,6 +116,20 @@ limitations under the License.
           storageSync.remove(['disableTextLayer', 'enhanceTextSelection']);
         }
       }
+      // Migration code for https://github.com/mozilla/pdf.js/pull/10502.
+      if (typeof items.showPreviousViewOnLoad === 'boolean') {
+        if (!items.showPreviousViewOnLoad) {
+          storageSync.set({
+            viewOnLoad: 1,
+          }, function() {
+            if (!chrome.runtime.lastError) {
+              storageSync.remove(['showPreviousViewOnLoad', 'disablePageMode']);
+            }
+          });
+        } else {
+          storageSync.remove(['showPreviousViewOnLoad', 'disablePageMode']);
+        }
+      }
     });
   }
 })();
diff --git a/extensions/chromium/options/options.html b/extensions/chromium/options/options.html
index 412e80bb1a11c..57ddae7b14305 100644
--- a/extensions/chromium/options/options.html
+++ b/extensions/chromium/options/options.html
@@ -43,6 +43,19 @@
 </div>
 </template>
 
+<template id="viewOnLoad-template">
+<div class="settings-row">
+  <label>
+    <span></span>
+    <select>
+      <option value="-1">Default</option>
+      <option value="0">Show previous position</option>
+      <option value="1">Show initial position</option>
+    </select>
+  </label>
+</div>
+</template>
+
 <template id="defaultZoomValue-template">
 <div class="settings-row">
   <label>
@@ -71,6 +84,7 @@
   <label>
     <span></span>
     <select>
+      <option value="-1">Default</option>
       <option value="0">Do not show sidebar</option>
       <option value="1">Show thumbnails in sidebar</option>
       <option value="2">Show document outline in sidebar</option>
@@ -125,6 +139,7 @@
   <label>
     <span></span>
     <select>
+      <option value="-1">Default</option>
       <option value="0">Vertical scrolling</option>
       <option value="1">Horizontal scrolling</option>
       <option value="2">Wrapped scrolling</option>
@@ -138,6 +153,7 @@
   <label>
     <span></span>
     <select>
+      <option value="-1">Default</option>
       <option value="0">No spreads</option>
       <option value="1">Odd spreads</option>
       <option value="2">Even spreads</option>
diff --git a/extensions/chromium/preferences_schema.json b/extensions/chromium/preferences_schema.json
index eb264dee26999..2ce2a53ba4080 100644
--- a/extensions/chromium/preferences_schema.json
+++ b/extensions/chromium/preferences_schema.json
@@ -2,11 +2,20 @@
   "type": "object",
   "properties": {
     "showPreviousViewOnLoad": {
-      "title": "Show previous position of PDF upon load",
-      "description": "Whether to view PDF documents in the last page and position upon opening the viewer.",
+      "description": "DEPRECATED. Set viewOnLoad to 1 to disable showing the last page/position on load.",
       "type": "boolean",
       "default": true
     },
+    "viewOnLoad": {
+      "title": "View position on load",
+      "description": "The position in the document upon load.\n -1 = Default (uses OpenAction if available, otherwise equal to `viewOnLoad = 0`).\n 0 = The last viewed page/position.\n 1 = The initial page/position.",
+      "enum": [
+        -1,
+        0,
+        1
+      ],
+      "default": 0
+    },
     "defaultZoomValue": {
       "title": "Default zoom level",
       "description": "Default zoom level of the viewer. Accepted values: 'auto', 'page-actual', 'page-width', 'page-height', 'page-fit', or a zoom level in percents.",
@@ -16,15 +25,16 @@
     },
     "sidebarViewOnLoad": {
       "title": "Sidebar state on load",
-      "description": "Controls the state of the sidebar upon load.\n 0 = do not show sidebar.\n 1 = show thumbnails in sidebar.\n 2 = show document outline in sidebar.\n 3 = Show attachments in sidebar.",
+      "description": "Controls the state of the sidebar upon load.\n -1 = Default (uses PageMode if available, otherwise the last position if available/enabled).\n 0 = Do not show sidebar.\n 1 = Show thumbnails in sidebar.\n 2 = Show document outline in sidebar.\n 3 = Show attachments in sidebar.",
       "type": "integer",
       "enum": [
+        -1,
         0,
         1,
         2,
         3
       ],
-      "default": 0
+      "default": -1
     },
     "enableHandToolOnLoad": {
       "description": "DEPRECATED. Set cursorToolOnLoad to 1 to enable the hand tool by default.",
@@ -117,15 +127,12 @@
       ],
       "default": 0
     },
-    "disableOpenActionDestination": {
-      "type": "boolean",
-      "default": true
-    },
     "disablePageLabels": {
       "type": "boolean",
       "default": false
     },
     "disablePageMode": {
+      "description": "DEPRECATED.",
       "type": "boolean",
       "default": false
     },
@@ -159,25 +166,27 @@
     },
     "scrollModeOnLoad": {
       "title": "Scroll mode on load",
-      "description": "Controls how the viewer scrolls upon load.\n 0 = Vertical scrolling.\n 1 = Horizontal scrolling.\n 2 = Wrapped scrolling.",
+      "description": "Controls how the viewer scrolls upon load.\n -1 = Default (uses the last position if available/enabled).\n 0 = Vertical scrolling.\n 1 = Horizontal scrolling.\n 2 = Wrapped scrolling.",
       "type": "integer",
       "enum": [
+        -1,
         0,
         1,
         2
       ],
-      "default": 0
+      "default": -1
     },
     "spreadModeOnLoad": {
       "title": "Spread mode on load",
-      "description": "Whether the viewer should join pages into spreads upon load.\n 0 = No spreads.\n 1 = Odd spreads.\n 2 = Even spreads.",
+      "description": "Whether the viewer should join pages into spreads upon load.\n -1 = Default (uses the last position if available/enabled).\n 0 = No spreads.\n 1 = Odd spreads.\n 2 = Even spreads.",
       "type": "integer",
       "enum": [
+        -1,
         0,
         1,
         2
       ],
-      "default": 0
+      "default": -1
     }
   }
 }
diff --git a/web/app.js b/web/app.js
index 0d09e67ef7536..5c87ee0d257a5 100644
--- a/web/app.js
+++ b/web/app.js
@@ -16,9 +16,10 @@
 
 import {
   animationStarted, DEFAULT_SCALE_VALUE, getGlobalEventBus,
-  getPDFFileNameFromURL, isValidRotation, MAX_SCALE, MIN_SCALE,
-  noContextMenuHandler, normalizeWheelEventDelta, parseQueryString,
-  PresentationModeState, ProgressBar, RendererType, TextLayerMode
+  getPDFFileNameFromURL, isValidRotation, isValidScrollMode, isValidSpreadMode,
+  MAX_SCALE, MIN_SCALE, noContextMenuHandler, normalizeWheelEventDelta,
+  parseQueryString, PresentationModeState, ProgressBar, RendererType,
+  ScrollMode, SpreadMode, TextLayerMode
 } from './ui_utils';
 import {
   build, createObjectURL, getDocument, getFilenameFromUrl, GlobalWorkerOptions,
@@ -52,6 +53,12 @@ const DISABLE_AUTO_FETCH_LOADING_BAR_TIMEOUT = 5000; // ms
 const FORCE_PAGES_LOADED_TIMEOUT = 10000; // ms
 const WHEEL_ZOOM_DISABLED_TIMEOUT = 1000; // ms
 
+const ViewOnLoad = {
+  UNKNOWN: -1,
+  PREVIOUS: 0, // Default value.
+  INITIAL: 1,
+};
+
 const DefaultExternalServices = {
   updateFindControlState(data) {},
   updateFindMatchesCount(data) {},
@@ -900,46 +907,29 @@ let PDFViewerApplication = {
     firstPagePromise.then((pdfPage) => {
       this.loadingBar.setWidth(this.appConfig.viewerContainer);
 
-      if (!AppOptions.get('disableHistory') && !this.isViewerEmbedded) {
-        // The browsing history is only enabled when the viewer is standalone,
-        // i.e. not when it is embedded in a web page.
-        this.pdfHistory.initialize({
-          fingerprint: pdfDocument.fingerprint,
-          resetHistory: !AppOptions.get('showPreviousViewOnLoad'),
-          updateUrl: AppOptions.get('historyUpdateUrl'),
-        });
-
-        if (this.pdfHistory.initialBookmark) {
-          this.initialBookmark = this.pdfHistory.initialBookmark;
-
-          this.initialRotation = this.pdfHistory.initialRotation;
-        }
-      }
-
-      let storePromise = store.getMultiple({
+      const storePromise = store.getMultiple({
         page: null,
         zoom: DEFAULT_SCALE_VALUE,
         scrollLeft: '0',
         scrollTop: '0',
         rotation: null,
-        sidebarView: SidebarView.NONE,
-        scrollMode: null,
-        spreadMode: null,
+        sidebarView: SidebarView.UNKNOWN,
+        scrollMode: ScrollMode.UNKNOWN,
+        spreadMode: SpreadMode.UNKNOWN,
       }).catch(() => { /* Unable to read from storage; ignoring errors. */ });
 
       Promise.all([
         storePromise, pageModePromise, openActionDestPromise,
       ]).then(async ([values = {}, pageMode, openActionDest]) => {
-        if (openActionDest && !this.initialBookmark &&
-            !AppOptions.get('disableOpenActionDestination')) {
-          // Always let the browser history/document hash take precedence.
-          this.initialBookmark = JSON.stringify(openActionDest);
-          // TODO: Re-factor the `PDFHistory` initialization to remove this hack
-          // that's currently necessary to prevent weird initial history state.
-          this.pdfHistory.push({ explicitDest: openActionDest,
-                                 pageNumber: null, });
-        }
+        const viewOnLoad = AppOptions.get('viewOnLoad');
+
+        this._initializePdfHistory({
+          fingerprint: pdfDocument.fingerprint,
+          viewOnLoad,
+          initialDest: openActionDest,
+        });
         const initialBookmark = this.initialBookmark;
+
         // Initialize the default values, from user preferences.
         const zoom = AppOptions.get('defaultZoomValue');
         let hash = zoom ? `zoom=${zoom}` : null;
@@ -949,18 +939,25 @@ let PDFViewerApplication = {
         let scrollMode = AppOptions.get('scrollModeOnLoad');
         let spreadMode = AppOptions.get('spreadModeOnLoad');
 
-        if (values.page && AppOptions.get('showPreviousViewOnLoad')) {
-          hash = 'page=' + values.page + '&zoom=' + (zoom || values.zoom) +
-            ',' + values.scrollLeft + ',' + values.scrollTop;
+        if (values.page && viewOnLoad !== ViewOnLoad.INITIAL) {
+          hash = `page=${values.page}&zoom=${zoom || values.zoom},` +
+                 `${values.scrollLeft},${values.scrollTop}`;
 
           rotation = parseInt(values.rotation, 10);
-          sidebarView = sidebarView || (values.sidebarView | 0);
-          scrollMode = scrollMode || (values.scrollMode | 0);
-          spreadMode = spreadMode || (values.spreadMode | 0);
+          // Always let user preferences take precedence over the view history.
+          if (sidebarView === SidebarView.UNKNOWN) {
+            sidebarView = (values.sidebarView | 0);
+          }
+          if (scrollMode === ScrollMode.UNKNOWN) {
+            scrollMode = (values.scrollMode | 0);
+          }
+          if (spreadMode === SpreadMode.UNKNOWN) {
+            spreadMode = (values.spreadMode | 0);
+          }
         }
-        if (pageMode && !AppOptions.get('disablePageMode')) {
-          // Always let the user preference/history take precedence.
-          sidebarView = sidebarView || apiPageModeToSidebarView(pageMode);
+        // Always let the user preference/view history take precedence.
+        if (pageMode && sidebarView === SidebarView.UNKNOWN) {
+          sidebarView = apiPageModeToSidebarView(pageMode);
         }
 
         this.setInitialView(hash, {
@@ -1147,30 +1144,57 @@ let PDFViewerApplication = {
     });
   },
 
+  /**
+   * @private
+   */
+  _initializePdfHistory({ fingerprint, viewOnLoad, initialDest = null, }) {
+    if (AppOptions.get('disableHistory') || this.isViewerEmbedded) {
+      // The browsing history is only enabled when the viewer is standalone,
+      // i.e. not when it is embedded in a web page.
+      return;
+    }
+    this.pdfHistory.initialize({
+      fingerprint,
+      resetHistory: viewOnLoad === ViewOnLoad.INITIAL,
+      updateUrl: AppOptions.get('historyUpdateUrl'),
+    });
+
+    if (this.pdfHistory.initialBookmark) {
+      this.initialBookmark = this.pdfHistory.initialBookmark;
+
+      this.initialRotation = this.pdfHistory.initialRotation;
+    }
+
+    // Always let the browser history/document hash take precedence.
+    if (initialDest && !this.initialBookmark &&
+        viewOnLoad === ViewOnLoad.UNKNOWN) {
+      this.initialBookmark = JSON.stringify(initialDest);
+      // TODO: Re-factor the `PDFHistory` initialization to remove this hack
+      // that's currently necessary to prevent weird initial history state.
+      this.pdfHistory.push({ explicitDest: initialDest, pageNumber: null, });
+    }
+  },
+
   setInitialView(storedHash, { rotation, sidebarView,
                                scrollMode, spreadMode, } = {}) {
-    let setRotation = (angle) => {
+    const setRotation = (angle) => {
       if (isValidRotation(angle)) {
         this.pdfViewer.pagesRotation = angle;
       }
     };
-    let setViewerModes = (scroll, spread) => {
-      if (Number.isInteger(scroll)) {
+    const setViewerModes = (scroll, spread) => {
+      if (isValidScrollMode(scroll)) {
         this.pdfViewer.scrollMode = scroll;
       }
-      if (Number.isInteger(spread)) {
+      if (isValidSpreadMode(spread)) {
         this.pdfViewer.spreadMode = spread;
       }
     };
-
-    // Putting these before isInitialViewSet = true prevents these values from
-    // being stored in the document history (and overriding any future changes
-    // made to the corresponding global preferences), just this once.
-    setViewerModes(scrollMode, spreadMode);
-
     this.isInitialViewSet = true;
     this.pdfSidebar.setInitialView(sidebarView);
 
+    setViewerModes(scrollMode, spreadMode);
+
     if (this.initialBookmark) {
       setRotation(this.initialRotation);
       delete this.initialRotation;
diff --git a/web/app_options.js b/web/app_options.js
index 7e98646231238..12686d38b7acc 100644
--- a/web/app_options.js
+++ b/web/app_options.js
@@ -48,21 +48,11 @@ const defaultOptions = {
     value: false,
     kind: OptionKind.VIEWER,
   },
-  disableOpenActionDestination: {
-    /** @type {boolean} */
-    value: true,
-    kind: OptionKind.VIEWER,
-  },
   disablePageLabels: {
     /** @type {boolean} */
     value: false,
     kind: OptionKind.VIEWER,
   },
-  disablePageMode: {
-    /** @type {boolean} */
-    value: false,
-    kind: OptionKind.VIEWER,
-  },
   /**
    * The `disablePreferences` is, conditionally, defined below.
    */
@@ -106,7 +96,8 @@ const defaultOptions = {
    */
   maxCanvasPixels: {
     /** @type {number} */
-    value: viewerCompatibilityParams.maxCanvasPixels || 16777216,
+    value: 16777216,
+    compatibility: viewerCompatibilityParams.maxCanvasPixels,
     kind: OptionKind.VIEWER,
   },
   pdfBugEnabled: {
@@ -124,24 +115,19 @@ const defaultOptions = {
     value: false,
     kind: OptionKind.VIEWER,
   },
-  showPreviousViewOnLoad: {
-    /** @type {boolean} */
-    value: true,
-    kind: OptionKind.VIEWER,
-  },
   sidebarViewOnLoad: {
     /** @type {number} */
-    value: 0,
+    value: -1,
     kind: OptionKind.VIEWER,
   },
   scrollModeOnLoad: {
     /** @type {number} */
-    value: 0,
+    value: -1,
     kind: OptionKind.VIEWER,
   },
   spreadModeOnLoad: {
     /** @type {number} */
-    value: 0,
+    value: -1,
     kind: OptionKind.VIEWER,
   },
   textLayerMode: {
@@ -154,6 +140,11 @@ const defaultOptions = {
     value: false,
     kind: OptionKind.VIEWER,
   },
+  viewOnLoad: {
+    /** @type {boolean} */
+    value: 0,
+    kind: OptionKind.VIEWER,
+  },
 
   cMapPacked: {
     /** @type {boolean} */
@@ -173,7 +164,8 @@ const defaultOptions = {
   },
   disableCreateObjectURL: {
     /** @type {boolean} */
-    value: apiCompatibilityParams.disableCreateObjectURL || false,
+    value: false,
+    compatibility: apiCompatibilityParams.disableCreateObjectURL,
     kind: OptionKind.API,
   },
   disableFontFace: {
@@ -251,22 +243,27 @@ class AppOptions {
   }
 
   static get(name) {
-    let defaultOption = defaultOptions[name], userOption = userOptions[name];
+    const userOption = userOptions[name];
     if (userOption !== undefined) {
       return userOption;
     }
-    return (defaultOption !== undefined ? defaultOption.value : undefined);
+    const defaultOption = defaultOptions[name];
+    if (defaultOption !== undefined) {
+      return (defaultOption.compatibility || defaultOption.value);
+    }
+    return undefined;
   }
 
   static getAll(kind = null) {
-    let options = Object.create(null);
-    for (let name in defaultOptions) {
-      let defaultOption = defaultOptions[name], userOption = userOptions[name];
-      if (kind && defaultOption.kind !== kind) {
+    const options = Object.create(null);
+    for (const name in defaultOptions) {
+      const defaultOption = defaultOptions[name];
+      if (kind && kind !== defaultOption.kind) {
         continue;
       }
-      options[name] = (userOption !== undefined ?
-                       userOption : defaultOption.value);
+      const userOption = userOptions[name];
+      options[name] = (userOption !== undefined ? userOption :
+                       (defaultOption.compatibility || defaultOption.value));
     }
     return options;
   }
diff --git a/web/base_viewer.js b/web/base_viewer.js
index 416602dca8deb..45578ac850cc2 100644
--- a/web/base_viewer.js
+++ b/web/base_viewer.js
@@ -15,10 +15,11 @@
 
 import {
   CSS_UNITS, DEFAULT_SCALE, DEFAULT_SCALE_VALUE, getGlobalEventBus,
-  getVisibleElements, isPortraitOrientation, isValidRotation, MAX_AUTO_SCALE,
-  moveToEndOfArray, NullL10n, PresentationModeState, RendererType,
-  SCROLLBAR_PADDING, scrollIntoView, TextLayerMode, UNKNOWN_SCALE,
-  VERTICAL_PADDING, watchScroll
+  getVisibleElements, isPortraitOrientation, isValidRotation, isValidScrollMode,
+  isValidSpreadMode, MAX_AUTO_SCALE, moveToEndOfArray, NullL10n,
+  PresentationModeState, RendererType, SCROLLBAR_PADDING, scrollIntoView,
+  ScrollMode, SpreadMode, TextLayerMode, UNKNOWN_SCALE, VERTICAL_PADDING,
+  watchScroll
 } from './ui_utils';
 import { PDFRenderingQueue, RenderingStates } from './pdf_rendering_queue';
 import { AnnotationLayerBuilder } from './annotation_layer_builder';
@@ -29,18 +30,6 @@ import { TextLayerBuilder } from './text_layer_builder';
 
 const DEFAULT_CACHE_SIZE = 10;
 
-const ScrollMode = {
-  VERTICAL: 0, // The default value.
-  HORIZONTAL: 1,
-  WRAPPED: 2,
-};
-
-const SpreadMode = {
-  NONE: 0, // The default value.
-  ODD: 1,
-  EVEN: 2,
-};
-
 /**
  * @typedef {Object} PDFViewerOptions
  * @property {HTMLDivElement} container - The container for the viewer element.
@@ -1084,7 +1073,7 @@ class BaseViewer {
     if (this._scrollMode === mode) {
       return; // The Scroll mode didn't change.
     }
-    if (!Number.isInteger(mode) || !Object.values(ScrollMode).includes(mode)) {
+    if (!isValidScrollMode(mode)) {
       throw new Error(`Invalid scroll mode: ${mode}`);
     }
     this._scrollMode = mode;
@@ -1130,7 +1119,7 @@ class BaseViewer {
     if (this._spreadMode === mode) {
       return; // The Spread mode didn't change.
     }
-    if (!Number.isInteger(mode) || !Object.values(SpreadMode).includes(mode)) {
+    if (!isValidSpreadMode(mode)) {
       throw new Error(`Invalid spread mode: ${mode}`);
     }
     this._spreadMode = mode;
@@ -1177,6 +1166,4 @@ class BaseViewer {
 
 export {
   BaseViewer,
-  ScrollMode,
-  SpreadMode,
 };
diff --git a/web/chromecom.js b/web/chromecom.js
index 48eecb6ccc35e..88c8f525921fe 100644
--- a/web/chromecom.js
+++ b/web/chromecom.js
@@ -341,6 +341,8 @@ class ChromePreferences extends BasePreferences {
           enableHandToolOnLoad: false,
           disableTextLayer: false,
           enhanceTextSelection: false,
+          showPreviousViewOnLoad: true,
+          disablePageMode: false,
         }, this.defaults);
 
         chrome.storage.managed.get(defaultManagedPrefs, function(items) {
@@ -370,6 +372,13 @@ class ChromePreferences extends BasePreferences {
           delete items.disableTextLayer;
           delete items.enhanceTextSelection;
 
+          // Migration code for https://github.com/mozilla/pdf.js/pull/10502.
+          if (!items.showPreviousViewOnLoad && !items.viewOnLoad) {
+            items.viewOnLoad = 1;
+          }
+          delete items.showPreviousViewOnLoad;
+          delete items.disablePageMode;
+
           getPreferences(items);
         });
       } else {
diff --git a/web/default_preferences.json b/web/default_preferences.json
index 702b5d5a970d2..22a115b44a754 100644
--- a/web/default_preferences.json
+++ b/web/default_preferences.json
@@ -1,7 +1,7 @@
 {
-  "showPreviousViewOnLoad": true,
+  "viewOnLoad": 0,
   "defaultZoomValue": "",
-  "sidebarViewOnLoad": 0,
+  "sidebarViewOnLoad": -1,
   "cursorToolOnLoad": 0,
   "enableWebGL": false,
   "eventBusDispatchToDOM": false,
@@ -16,10 +16,8 @@
   "renderer": "canvas",
   "renderInteractiveForms": false,
   "enablePrintAutoRotate": false,
-  "disableOpenActionDestination": true,
-  "disablePageMode": false,
   "disablePageLabels": false,
   "historyUpdateUrl": false,
-  "scrollModeOnLoad": 0,
-  "spreadModeOnLoad": 0
+  "scrollModeOnLoad": -1,
+  "spreadModeOnLoad": -1
 }
diff --git a/web/pdf_sidebar.js b/web/pdf_sidebar.js
index 27a77ad59b11b..80c5b31449d1a 100644
--- a/web/pdf_sidebar.js
+++ b/web/pdf_sidebar.js
@@ -19,10 +19,12 @@ import { RenderingStates } from './pdf_rendering_queue';
 const UI_NOTIFICATION_CLASS = 'pdfSidebarNotification';
 
 const SidebarView = {
+  UNKNOWN: -1,
   NONE: 0,
-  THUMBS: 1,
+  THUMBS: 1, // Default value.
   OUTLINE: 2,
   ATTACHMENTS: 3,
+  LAYERS: 4,
 };
 
 /**
@@ -130,18 +132,15 @@ class PDFSidebar {
     }
     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; also ignore the "unknown" sidebar view value.
+    if (view === SidebarView.NONE || view === SidebarView.UNKNOWN) {
       this._dispatchEvent();
-      // If the user has already manually opened the sidebar,
-      // immediately closing it would be bad UX.
       return;
     }
-    let isViewPreserved = (view === this.visibleView);
-    this.switchView(view, /* forceOpen */ true);
-
-    if (isViewPreserved) {
-      // Prevent dispatching two back-to-back `sidebarviewchanged` events,
-      // since `this.switchView` dispatched the event if the view changed.
+    // Prevent dispatching two back-to-back `sidebarviewchanged` events,
+    // since `this._switchView` dispatched the event if the view changed.
+    if (!this._switchView(view, /* forceOpen */ true)) {
       this._dispatchEvent();
     }
   }
@@ -153,14 +152,24 @@ class PDFSidebar {
    *                              The default value is `false`.
    */
   switchView(view, forceOpen = false) {
-    if (view === SidebarView.NONE) {
-      this.close();
-      return;
-    }
-    let isViewChanged = (view !== this.active);
+    this._switchView(view, forceOpen);
+  }
+
+  /**
+   * @returns {boolean} Indicating if `this._dispatchEvent` was called.
+   * @private
+   */
+  _switchView(view, forceOpen = false) {
+    const isViewChanged = (view !== this.active);
     let shouldForceRendering = false;
 
     switch (view) {
+      case SidebarView.NONE:
+        if (this.isOpen) {
+          this.close();
+          return true; // Closing will trigger rendering and dispatch the event.
+        }
+        return false;
       case SidebarView.THUMBS:
         this.thumbnailButton.classList.add('toggled');
         this.outlineButton.classList.remove('toggled');
@@ -177,7 +186,7 @@ class PDFSidebar {
         break;
       case SidebarView.OUTLINE:
         if (this.outlineButton.disabled) {
-          return;
+          return false;
         }
         this.thumbnailButton.classList.remove('toggled');
         this.outlineButton.classList.add('toggled');
@@ -189,7 +198,7 @@ class PDFSidebar {
         break;
       case SidebarView.ATTACHMENTS:
         if (this.attachmentsButton.disabled) {
-          return;
+          return false;
         }
         this.thumbnailButton.classList.remove('toggled');
         this.outlineButton.classList.remove('toggled');
@@ -200,9 +209,8 @@ class PDFSidebar {
         this.attachmentsView.classList.remove('hidden');
         break;
       default:
-        console.error('PDFSidebar_switchView: "' + view +
-                      '" is an unsupported value.');
-        return;
+        console.error(`PDFSidebar._switchView: "${view}" is not a valid view.`);
+        return false;
     }
     // Update the active view *after* it has been validated above,
     // in order to prevent setting it to an invalid state.
@@ -210,7 +218,7 @@ class PDFSidebar {
 
     if (forceOpen && !this.isOpen) {
       this.open();
-      return; // NOTE: Opening will trigger rendering, and dispatch the event.
+      return true; // Opening will trigger rendering and dispatch the event.
     }
     if (shouldForceRendering) {
       this._forceRendering();
@@ -219,6 +227,7 @@ class PDFSidebar {
       this._dispatchEvent();
     }
     this._hideUINotification(this.active);
+    return isViewChanged;
   }
 
   open() {
diff --git a/web/secondary_toolbar.js b/web/secondary_toolbar.js
index b9f6f6701d9fd..4c4c679e75901 100644
--- a/web/secondary_toolbar.js
+++ b/web/secondary_toolbar.js
@@ -13,10 +13,9 @@
  * limitations under the License.
  */
 
-import { ScrollMode, SpreadMode } from './base_viewer';
+import { SCROLLBAR_PADDING, ScrollMode, SpreadMode } from './ui_utils';
 import { CursorTool } from './pdf_cursor_tools';
 import { PDFSinglePageViewer } from './pdf_single_page_viewer';
-import { SCROLLBAR_PADDING } from './ui_utils';
 
 /**
  * @typedef {Object} SecondaryToolbarOptions
diff --git a/web/ui_utils.js b/web/ui_utils.js
index f2d9bb05811a1..e1235759ae5ba 100644
--- a/web/ui_utils.js
+++ b/web/ui_utils.js
@@ -41,6 +41,20 @@ const TextLayerMode = {
   ENABLE_ENHANCE: 2,
 };
 
+const ScrollMode = {
+  UNKNOWN: -1,
+  VERTICAL: 0, // Default value.
+  HORIZONTAL: 1,
+  WRAPPED: 2,
+};
+
+const SpreadMode = {
+  UNKNOWN: -1,
+  NONE: 0, // Default value.
+  ODD: 1,
+  EVEN: 2,
+};
+
 // Replaces {{arguments}} with their values.
 function formatL10nValue(text, args) {
   if (!args) {
@@ -602,6 +616,16 @@ function isValidRotation(angle) {
   return Number.isInteger(angle) && angle % 90 === 0;
 }
 
+function isValidScrollMode(mode) {
+  return (Number.isInteger(mode) && Object.values(ScrollMode).includes(mode) &&
+          mode !== ScrollMode.UNKNOWN);
+}
+
+function isValidSpreadMode(mode) {
+  return (Number.isInteger(mode) && Object.values(SpreadMode).includes(mode) &&
+          mode !== SpreadMode.UNKNOWN);
+}
+
 function isPortraitOrientation(size) {
   return size.width <= size.height;
 }
@@ -863,10 +887,14 @@ export {
   SCROLLBAR_PADDING,
   VERTICAL_PADDING,
   isValidRotation,
+  isValidScrollMode,
+  isValidSpreadMode,
   isPortraitOrientation,
   PresentationModeState,
   RendererType,
   TextLayerMode,
+  ScrollMode,
+  SpreadMode,
   NullL10n,
   EventBus,
   getGlobalEventBus,