diff --git a/chrome/content/zotero/components/itemPane/notesList.jsx b/chrome/content/zotero/components/itemPane/notesList.jsx
index aced7d0b3b..08611e5ca8 100644
--- a/chrome/content/zotero/components/itemPane/notesList.jsx
+++ b/chrome/content/zotero/components/itemPane/notesList.jsx
@@ -26,7 +26,7 @@
 import React, { forwardRef, useImperativeHandle, useState, memo } from 'react';
 import cx from 'classnames';
 
-const MAX_ALL_NOTES = 7;
+const MAX_UNEXPANDED_ALL_NOTES = 7;
 
 const NoteRow = memo(({ id, title, body, date, onClick, onContextMenu, parentItemType, parentTitle }) => {
 	return (
@@ -54,15 +54,32 @@ const NoteRow = memo(({ id, title, body, date, onClick, onContextMenu, parentIte
 const NotesList = forwardRef(({ onClick, onContextMenu, onAddChildButtonDown, onAddStandaloneButtonDown }, ref) => {
 	const [notes, setNotes] = useState([]);
 	const [expanded, setExpanded] = useState(false);
+	const [numVisible, setNumVisible] = useState(0);
 	const [hasParent, setHasParent] = useState(true);
-	useImperativeHandle(ref, () => ({ setNotes, setExpanded, setHasParent }));
+
+	const _setExpanded = (value) => {
+		setExpanded(value);
+		if (value) {
+			setNumVisible(numVisible + 1000);
+		}
+		else {
+			setNumVisible(0);
+		}
+	};
+	
+	useImperativeHandle(ref, () => ({
+		setNotes,
+		setHasParent,
+		setExpanded: _setExpanded
+	}));
 	
 	function handleClickMore() {
-		setExpanded(true);
+		_setExpanded(true);
 	}
 	
 	let childNotes = notes.filter(x => x.isCurrentChild);
 	let allNotes = notes.filter(x => !x.isCurrentChild);
+	let visibleNotes = allNotes.slice(0, expanded ? numVisible : MAX_UNEXPANDED_ALL_NOTES);
 	return (
 		<div className="notes-list">
 			{hasParent && <section>
@@ -80,12 +97,12 @@ const NotesList = forwardRef(({ onClick, onContextMenu, onAddChildButtonDown, on
 					<button onMouseDown={onAddStandaloneButtonDown}>+</button>
 				</div>
 				{!allNotes.length && <div className="empty-row">{Zotero.getString('pane.context.noNotes')}</div>}
-				{(expanded ? allNotes : allNotes.slice(0, MAX_ALL_NOTES))
-					.map(note => <NoteRow key={note.id} {...note}
-						onClick={onClick} onContextMenu={onContextMenu}/>)}
-				{!expanded && allNotes.length > MAX_ALL_NOTES
+				{visibleNotes.map(note => <NoteRow key={note.id} {...note}
+					onClick={onClick} onContextMenu={onContextMenu}/>)}
+				{allNotes.length > visibleNotes.length
 					&& <div className="more-row" onClick={handleClickMore}>{
-						Zotero.getString('general.numMore', Zotero.Utilities.numberFormat([allNotes.length - MAX_ALL_NOTES], 0))
+						Zotero.getString('general.numMore', Zotero.Utilities.numberFormat(
+							[(allNotes.length - visibleNotes.length) - MAX_UNEXPANDED_ALL_NOTES], 0))
 					}</div>
 				}
 			</section>
diff --git a/chrome/content/zotero/contextPane.js b/chrome/content/zotero/contextPane.js
index 67a9e0c41a..9b65b5205a 100644
--- a/chrome/content/zotero/contextPane.js
+++ b/chrome/content/zotero/contextPane.js
@@ -156,6 +156,9 @@ var ZoteroContextPane = new function () {
 				}
 			}
 			else if (action == 'select') {
+				// It seems that changing `hidden` or `collapsed` values might
+				// be related with significant slow down when there are too many
+				// DOM nodes (i.e. 10k notes)
 				if (Zotero_Tabs.selectedIndex == 0) {
 					_contextPaneSplitter.setAttribute('hidden', true);
 					_contextPane.setAttribute('collapsed', true);
@@ -470,9 +473,27 @@ var ZoteroContextPane = new function () {
 
 		var notesListRef = React.createRef();
 
+		function _isVisible() {
+			let splitter = Zotero.Prefs.get('layout') == 'stacked'
+				? _contextPaneSplitterStacked : _contextPaneSplitter;
+			
+			return Zotero_Tabs.selectedID != 'zotero-pane'
+				&& _panesDeck.selectedIndex == 1
+				&& context.node.selectedIndex == 0
+				&& splitter.getAttribute('state') != 'collapsed';
+		}
+
 		async function _updateNotesList(useCached) {
 			var query = input.value;
 			var notes;
+			
+			// Calls itself and debounces until notes list becomes
+			// visible, and then updates
+			if (!useCached && !_isVisible()) {
+				context.update();
+				return;
+			}
+			
 			if (useCached && context.cachedNotes.length) {
 				notes = context.cachedNotes;
 			}
@@ -490,22 +511,25 @@ var ZoteroContextPane = new function () {
 				notes = await s.search();
 				notes = Zotero.Items.get(notes);
 				notes.sort((a, b) => {
-					a = a.getField('dateModified');
-					b = b.getField('dateModified');
-					return b.localeCompare(a);
+					a = a.dateModified;
+					b = b.dateModified;
+					return (a > b ? -1 : (a < b ? 1 : 0));
 				});
 				
+				let cachedNotesIndex = new Map();
+				for (let cachedNote of context.cachedNotes) {
+					cachedNotesIndex.set(cachedNote.id, cachedNote);
+				}
 				notes = notes.map(note => {
 					var parentItem = note.parentItem;
 					// If neither note nor parent item is affected try to return the cached note
 					if (!context.affectedIDs.has(note.id)
 						&& (!parentItem || !context.affectedIDs.has(parentItem.id))) {
-						let cachedNote = context.cachedNotes.find(x => x.id == note.id);
+						let cachedNote = cachedNotesIndex.get(note.id);
 						if (cachedNote) {
 							return cachedNote;
 						}
 					}
-
 					var text = note.note;
 					text = Zotero.Utilities.unescapeHTML(text);
 					text = text.trim();
@@ -513,7 +537,6 @@ var ZoteroContextPane = new function () {
 					var parts = text.split('\n').map(x => x.trim()).filter(x => x.length);
 					var title = parts[0] && parts[0].slice(0, Zotero.Notes.MAX_TITLE_LENGTH);
 					var date = Zotero.Date.sqlToDate(note.dateModified, true);
-					// This takes half of the CPU time
 					date = Zotero.Date.toFriendlyDate(date);
 					
 					return {
diff --git a/chrome/content/zotero/xpcom/date.js b/chrome/content/zotero/xpcom/date.js
index 848a6acc84..9f13c0fc0b 100644
--- a/chrome/content/zotero/xpcom/date.js
+++ b/chrome/content/zotero/xpcom/date.js
@@ -852,17 +852,28 @@ Zotero.Date = new function(){
 		return Zotero.getString("date.relative." + key + "." + (n ? "multiple" : "one"), n);
 	}
 	
+	// Initializing `toFriendlyDate` formatters, since
+	// `toLocaleDateString` is extremely slow (4500ms vs 200ms
+	// for 10k calls)
+	var _friendlyDateTodayFormatter = new Intl.DateTimeFormat(
+		false, { hour: 'numeric', minute: 'numeric' });
+
+	var _friendlyDateWeekFormatter = new Intl.DateTimeFormat(
+		false, { weekday: 'long' });
+
+	var _friendlyDateRegularFormatter = new Intl.DateTimeFormat(
+		false, { year: '2-digit', month: 'numeric', day: 'numeric' });
 	
 	this.toFriendlyDate = function (date) {
 		// 6:14:36 PM
 		if (isToday(date)) {
-			return date.toLocaleString(false, { hour: 'numeric', minute: 'numeric' })
+			return _friendlyDateTodayFormatter.format(date);
 		}
 		// 'Thursday'
 		if (isThisWeek(date)) {
-			return date.toLocaleString(false, { weekday: 'long' });
+			return _friendlyDateWeekFormatter.format(date);
 		}
-		return date.toLocaleDateString(false, { year: '2-digit', month: 'numeric', day: 'numeric' });
+		return _friendlyDateRegularFormatter.format(date);
 	};