diff --git a/src/Main.tsx b/src/Main.tsx
index af3d462a7..c90f016ac 100644
--- a/src/Main.tsx
+++ b/src/Main.tsx
@@ -105,9 +105,12 @@ const App = (): JSX.Element => {
   // Scenario-based health tracking: start ApplicationLoad and complete phases.
   const { startScenario, completePhase } = useMetricScenario();
   React.useEffect(() => {
-    startScenario(MetricScenario.ApplicationLoad);
-    // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, []);
+    // Only start scenario after config is initialized to avoid race conditions
+    // with message handlers that depend on configContext.platform
+    if (config) {
+      startScenario(MetricScenario.ApplicationLoad);
+    }
+  }, [config, startScenario]);
 
   React.useEffect(() => {
     if (explorer) {
diff --git a/src/NotebookViewer/NotebookViewer.tsx b/src/NotebookViewer/NotebookViewer.tsx
deleted file mode 100644
index 2bb1441b2..000000000
--- a/src/NotebookViewer/NotebookViewer.tsx
+++ /dev/null
@@ -1,88 +0,0 @@
-import { initializeIcons } from "@fluentui/react";
-import "bootstrap/dist/css/bootstrap.css";
-import React from "react";
-import * as ReactDOM from "react-dom";
-import { configContext, initializeConfiguration } from "../ConfigContext";
-import { GalleryHeaderComponent } from "../Explorer/Controls/Header/GalleryHeaderComponent";
-import { GalleryTab } from "../Explorer/Controls/NotebookGallery/GalleryViewerComponent";
-import {
-  NotebookViewerComponent,
-  NotebookViewerComponentProps,
-} from "../Explorer/Controls/NotebookViewer/NotebookViewerComponent";
-import * as FileSystemUtil from "../Explorer/Notebook/FileSystemUtil";
-import { IGalleryItem, JunoClient } from "../Juno/JunoClient";
-import * as GalleryUtils from "../Utils/GalleryUtils";
-
-const onInit = async () => {
-  initializeIcons();
-  await initializeConfiguration();
-  const galleryViewerProps = GalleryUtils.getGalleryViewerProps(window.location.search);
-  const notebookViewerProps = GalleryUtils.getNotebookViewerProps(window.location.search);
-  let backNavigationText: string;
-  let onBackClick: () => void;
-  if (galleryViewerProps.selectedTab !== undefined) {
-    backNavigationText = GalleryUtils.getTabTitle(galleryViewerProps.selectedTab);
-    onBackClick = () =>
-      (window.location.href = `${configContext.hostedExplorerURL}gallery.html?tab=${
-        GalleryTab[galleryViewerProps.selectedTab]
-      }`);
-  }
-  const hideInputs = notebookViewerProps.hideInputs;
-
-  const notebookUrl = decodeURIComponent(notebookViewerProps.notebookUrl);
-
-  const galleryItemId = notebookViewerProps.galleryItemId;
-  let galleryItem: IGalleryItem;
-
-  if (galleryItemId) {
-    const junoClient = new JunoClient();
-    const galleryItemJunoResponse = await junoClient.getNotebookInfo(galleryItemId);
-    galleryItem = galleryItemJunoResponse.data;
-  }
-
-  // The main purpose of hiding the prompt is to hide everything when hiding inputs.
-  // It is generally not very useful to just hide the prompt.
-  const hidePrompts = hideInputs;
-
-  render(notebookUrl, backNavigationText, hideInputs, hidePrompts, galleryItem, onBackClick);
-};
-
-const render = (
-  notebookUrl: string,
-  backNavigationText: string,
-  hideInputs?: boolean,
-  hidePrompts?: boolean,
-  galleryItem?: IGalleryItem,
-  onBackClick?: () => void,
-) => {
-  const props: NotebookViewerComponentProps = {
-    junoClient: galleryItem ? new JunoClient() : undefined,
-    notebookUrl,
-    galleryItem,
-    backNavigationText,
-    hideInputs,
-    hidePrompts,
-    onBackClick: onBackClick,
-    onTagClick: undefined,
-  };
-
-  if (galleryItem) {
-    document.title = FileSystemUtil.stripExtension(galleryItem.name, "ipynb");
-  }
-
-  const element = (
-    <>
-      <header>
-        <GalleryHeaderComponent />
-      </header>
-      <div style={{ marginLeft: 120, marginRight: 120 }}>
-        <NotebookViewerComponent {...props} />
-      </div>
-    </>
-  );
-
-  ReactDOM.render(element, document.getElementById("notebookContent"));
-};
-
-// Entry point
-window.addEventListener("load", onInit);
diff --git a/src/Platform/Hosted/extractFeatures.ts b/src/Platform/Hosted/extractFeatures.ts
index 2eecd5033..e9c4fc6b1 100644
--- a/src/Platform/Hosted/extractFeatures.ts
+++ b/src/Platform/Hosted/extractFeatures.ts
@@ -94,7 +94,7 @@ export function extractFeatures(given = new URLSearchParams(window.location.sear
     notebookBasePath: get("notebookbasepath"),
     notebookServerToken: get("notebookservertoken"),
     notebookServerUrl: get("notebookserverurl"),
-    sandboxNotebookOutputs: "true" === get("sandboxnotebookoutputs", "true"),
+    sandboxNotebookOutputs: true,
     selfServeType: get("selfservetype"),
     showMinRUSurvey: "true" === get("showminrusurvey"),
     ttl90Days: "true" === get("ttl90days"),
diff --git a/src/Utils/AuthorizationUtils.test.ts b/src/Utils/AuthorizationUtils.test.ts
index 781edec60..305b1cc9d 100644
--- a/src/Utils/AuthorizationUtils.test.ts
+++ b/src/Utils/AuthorizationUtils.test.ts
@@ -27,7 +27,7 @@ describe("AuthorizationUtils", () => {
         enableKoResourceTree: false,
         enableThroughputBuckets: false,
         hostedDataExplorer: false,
-        sandboxNotebookOutputs: false,
+        sandboxNotebookOutputs: true,
         showMinRUSurvey: false,
         ttl90Days: false,
         enableThroughputCap: false,