--- a/browser/components/extensions/ext-bookmarks.js
+++ b/browser/components/extensions/ext-bookmarks.js
@@ -2,16 +2,18 @@
 /* vim: set sts=2 sw=2 et tw=80: */
 "use strict";
 
 // The ext-* files are imported into the same scopes.
 /* import-globals-from ext-browserAction.js */
 
 XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
                                   "resource://gre/modules/PlacesUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PlacesUIUtils",
+                                  "resource:///modules/PlacesUIUtils.jsm");
 
 const {
   TYPE_BOOKMARK,
   TYPE_FOLDER,
   TYPE_SEPARATOR,
 } = PlacesUtils.bookmarks;
 
 const BOOKMARKS_TYPES_TO_API_TYPES_MAP = new Map([
@@ -111,22 +113,32 @@ const convertBookmarks = result => {
 };
 
 let observer = new class extends EventEmitter {
   constructor() {
     super();
 
     this.skipTags = true;
     this.skipDescendantsOnItemRemoval = true;
+    this.ignoreOnItemAdded = true;
+    this.virtualFolderIds = [PlacesUIUtils.leftPaneFolderId, PlacesUIUtils.allBookmarksFolderId];
+    this.ignoreOnItemAdded = false;
   }
 
   onBeginUpdateBatch() {}
   onEndUpdateBatch() {}
 
   onItemAdded(id, parentId, index, itemType, uri, title, dateAdded, guid, parentGuid, source) {
+    // Ignore Firefox's internal library folders.
+    if (this.ignoreOnItemAdded
+        || this.virtualFolderIds.includes(id)
+        || this.virtualFolderIds.includes(parentId)) {
+      return;
+    }
+
     let bookmark = {
       id: guid,
       parentId: parentGuid,
       index,
       title,
       dateAdded: dateAdded / 1000,
       type: BOOKMARKS_TYPES_TO_API_TYPES_MAP.get(itemType),
       url: getUrl(itemType, uri && uri.spec),