diff --git a/src/App.tsx b/src/App.tsx
index 4089b00..7839c93 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -17,6 +17,7 @@ import { TabMenu } from 'primereact/tabmenu';
 import { Badge } from 'primereact/badge';
 import { Menu } from 'primereact/menu';
 import { ToggleButton } from 'primereact/togglebutton';
+import { ConfirmDialog, confirmDialog } from 'primereact/confirmdialog';
 import { getParentDir } from './filesystem';
 import { BreadCrumb } from 'primereact/breadcrumb';
 import { ScrollPanel } from 'primereact/scrollpanel';
@@ -242,12 +243,31 @@ export function ViewerPanel({className, style}: {className?: string, style?: CSS
 
 function downloadOutput(state: State) {
   if (!state.output) return;
-  const a = document.createElement('a')
-  a.href = state.output.stlFileURL
-  a.download = state.output.isPreview ? 'preview.stl' : 'render.stl';
-  document.body.appendChild(a)
-  a.click()
-  document.body.removeChild(a)
+
+  const fileName = state.output!.isPreview ? 'preview.stl' : 'render.stl';
+  const doDownload = () => {
+    const a = document.createElement('a')
+    a.href = state.output!.stlFileURL
+    a.download = fileName;
+    document.body.appendChild(a)
+    a.click()
+    document.body.removeChild(a)
+  };
+
+  if (state.output.isPreview && state.params.source.indexOf('$preview') >= 0) {
+    confirmDialog({
+        message: "This model references the $preview variable but hasn't been rendered (F6), or its rendering is stale. You're about to download the preview result itself, which may not have the intended refinement of the render. Sure you want to proceed?",
+        header: 'Preview vs. Render',
+        icon: 'pi pi-exclamation-triangle',
+        accept: () => doDownload, 
+        acceptLabel: `Download ${fileName}`,
+        rejectLabel: 'Cancel'
+        // reject: () => {}
+    });
+  } else {
+    doDownload();
+  }
+
 }
 
 
@@ -333,6 +353,8 @@ function Footer({style}: {style?: CSSProperties}) {
       
       <span style={{flex: 1}}></span>
 
+      <ConfirmDialog />
+
       {state.output && (
         <Button icon='pi pi-download'
           title={`Download ${state.output.isPreview ? "preview.stl" : "render.stl"} (${state.output.formattedStlFileSize})`}
@@ -503,13 +525,14 @@ export function App({initialState, fs}: {initialState: State, fs: FS}) {
                           />
                         )}
                     </div>
-                :   <TabMenu 
-                style={{
-                  flex: 1,
-                  // justifyContent: 'center'
-                }}
-                model={singleTargets.map(({icon, label, id}) => 
-                ({icon, label, command: () => model.changeSingleVisibility(id)}))} />
+                :   <TabMenu
+                        activeIndex={singleTargets.map(t => t.id).indexOf(state.view.layout.focus)}
+                        style={{
+                          flex: 1,
+                          // justifyContent: 'center'
+                        }}
+                        model={singleTargets.map(({icon, label, id}) => 
+                            ({icon, label, disabled: id === 'customizer', command: () => model.changeSingleVisibility(id)}))} />
               }
             </div>
           </div>