diff --git a/packages/playground/website/src/lib/state/redux/slice-ui.ts b/packages/playground/website/src/lib/state/redux/slice-ui.ts
index 9b1f089d16..e248469263 100644
--- a/packages/playground/website/src/lib/state/redux/slice-ui.ts
+++ b/packages/playground/website/src/lib/state/redux/slice-ui.ts
@@ -127,6 +127,72 @@ export const listenToOnlineOfflineEventsMiddleware: Middleware =
 		return next(action);
 	};
 
+let browserConfirmationRanOnce = false;
+let hasUserInteracted = false;
+
+export const browserConfirmationMiddleware: Middleware =
+	(store) => (next) => (action) => {
+		if (!browserConfirmationRanOnce) {
+			browserConfirmationRanOnce = true;
+			if (typeof window !== 'undefined') {
+				// Track user interactions to avoid warning on quick open/close
+				const interactionEvents = [
+					'click',
+					'keypress',
+					'input',
+					'change',
+				];
+				interactionEvents.forEach((event) => {
+					window.addEventListener(
+						event,
+						() => {
+							hasUserInteracted = true;
+						},
+						{ once: true, capture: true }
+					);
+				});
+
+				window.addEventListener('beforeunload', (e) => {
+					// Don't warn if user hasn't interacted with the site
+					if (!hasUserInteracted) {
+						return;
+					}
+
+					// Check if WordPress editor already has unsaved changes
+					// If it does, let WordPress handle the confirmation
+					try {
+						const wpWindow = window as any;
+						if (
+							wpWindow.wp?.data
+								?.select?.('core/editor')
+								?.isEditedPostDirty?.()
+						) {
+							// WordPress will show its own dialog
+							return;
+						}
+					} catch {
+						// WordPress editor not available, continue with our check
+					}
+
+					const state = store.getState() as any;
+
+					// Check ALL temporary sites, not just the active one
+					const temporarySites = Object.values(
+						state.sites?.entities || {}
+					).filter((site: any) => site?.metadata?.storage === 'none');
+
+					// Only show confirmation if there are temporary sites
+					if (temporarySites.length > 0) {
+						e.preventDefault();
+						e.returnValue = '';
+						return '';
+					}
+				});
+			}
+		}
+		return next(action);
+	};
+
 export const {
 	setActiveModal,
 	setActiveSiteError,
diff --git a/packages/playground/website/src/lib/state/redux/store.ts b/packages/playground/website/src/lib/state/redux/store.ts
index 3ba04ed195..ac62e0e741 100644
--- a/packages/playground/website/src/lib/state/redux/store.ts
+++ b/packages/playground/website/src/lib/state/redux/store.ts
@@ -3,6 +3,7 @@ import type { SiteError } from './slice-ui';
 import uiReducer, {
 	__internal_uiSlice,
 	listenToOnlineOfflineEventsMiddleware,
+	browserConfirmationMiddleware,
 } from './slice-ui';
 import type { SiteInfo } from './slice-sites';
 import sitesReducer, {
@@ -61,7 +62,8 @@ const store = configureStore({
 	},
 	middleware: (getDefaultMiddleware) =>
 		ignoreSerializableCheck(getDefaultMiddleware).concat(
-			listenToOnlineOfflineEventsMiddleware
+			listenToOnlineOfflineEventsMiddleware,
+			browserConfirmationMiddleware
 		),
 });