diff --git a/web/pdf_attachment_viewer.js b/web/pdf_attachment_viewer.js
index eb4a3034be0d5..27d1b4eabb83f 100644
--- a/web/pdf_attachment_viewer.js
+++ b/web/pdf_attachment_viewer.js
@@ -35,13 +35,12 @@ class PDFAttachmentViewer {
    * @param {PDFAttachmentViewerOptions} options
    */
   constructor({ container, eventBus, downloadManager, }) {
-    this.attachments = null;
-
     this.container = container;
     this.eventBus = eventBus;
     this.downloadManager = downloadManager;
 
-    this._renderedCapability = createPromiseCapability();
+    this.reset();
+
     this.eventBus.on('fileattachmentannotation',
       this._appendAttachment.bind(this));
   }
@@ -63,12 +62,12 @@ class PDFAttachmentViewer {
    * @private
    */
   _dispatchEvent(attachmentsCount) {
+    this._renderedCapability.resolve();
+
     this.eventBus.dispatch('attachmentsloaded', {
       source: this,
       attachmentsCount,
     });
-
-    this._renderedCapability.resolve();
   }
 
   /**
diff --git a/web/pdf_outline_viewer.js b/web/pdf_outline_viewer.js
index 18d21471a928e..7aee5b626ddfe 100644
--- a/web/pdf_outline_viewer.js
+++ b/web/pdf_outline_viewer.js
@@ -36,12 +36,11 @@ class PDFOutlineViewer {
    * @param {PDFOutlineViewerOptions} options
    */
   constructor({ container, linkService, eventBus, }) {
-    this.outline = null;
-    this.lastToggleIsShow = true;
-
     this.container = container;
     this.linkService = linkService;
     this.eventBus = eventBus;
+
+    this.reset();
   }
 
   reset() {
diff --git a/web/pdf_sidebar.js b/web/pdf_sidebar.js
index f3a7a26f6d694..caabedd5738d7 100644
--- a/web/pdf_sidebar.js
+++ b/web/pdf_sidebar.js
@@ -420,17 +420,31 @@ class PDFSidebar {
     });
 
     this.eventBus.on('attachmentsloaded', (evt) => {
-      let attachmentsCount = evt.attachmentsCount;
+      if (evt.attachmentsCount) {
+        this.attachmentsButton.disabled = false;
 
-      this.attachmentsButton.disabled = !attachmentsCount;
-
-      if (attachmentsCount) {
         this._showUINotification(SidebarView.ATTACHMENTS);
-      } else if (this.active === SidebarView.ATTACHMENTS) {
-        // If the attachment view was opened during document load, switch away
-        // from it if it turns out that the document has no attachments.
-        this.switchView(SidebarView.THUMBS);
+        return;
       }
+
+      // Attempt to avoid temporarily disabling, and switching away from, the
+      // attachment view for documents that do not contain proper attachments
+      // but *only* FileAttachment annotations. Hence we defer those operations
+      // slightly to allow time for parsing any FileAttachment annotations that
+      // may be present on the *initially* rendered page of the document.
+      Promise.resolve().then(() => {
+        if (this.attachmentsView.hasChildNodes()) {
+          // FileAttachment annotations were appended to the attachment view.
+          return;
+        }
+        this.attachmentsButton.disabled = true;
+
+        if (this.active === SidebarView.ATTACHMENTS) {
+          // If the attachment view was opened during document load, switch away
+          // from it if it turns out that the document has no attachments.
+          this.switchView(SidebarView.THUMBS);
+        }
+      });
     });
 
     // Update the thumbnailViewer, if visible, when exiting presentation mode.