update

src/common/FilePreviewCommon/MarkdownHelper.cs

@@ -39,7 +39,7 @@ namespace Microsoft.PowerToys.FilePreviewCommon
             var softlineBreak = new Markdig.Extensions.Hardlines.SoftlineBreakAsHardlineExtension();
 
             MarkdownPipelineBuilder pipelineBuilder;
-            pipelineBuilder = new MarkdownPipelineBuilder().UseAdvancedExtensions().UseEmojiAndSmiley().UseYamlFrontMatter().UseMathematics().DisableHtml();
+            pipelineBuilder = new MarkdownPipelineBuilder().UseAdvancedExtensions().UseEmojiAndSmiley().UseYamlFrontMatter().UseMathematics();
             pipelineBuilder.Extensions.Add(extension);
             pipelineBuilder.Extensions.Add(softlineBreak);
 

src/modules/peek/Peek.FilePreviewer/Controls/BrowserControl.xaml.cs

@@ -74,6 +74,18 @@ namespace Peek.FilePreviewer.Controls
             }
         }
 
+        public static readonly DependencyProperty IsMarkdownProperty = DependencyProperty.Register(
+            nameof(IsMarkdown),
+            typeof(bool),
+            typeof(BrowserControl),
+            new PropertyMetadata(false));
+
+        public bool IsMarkdown
+        {
+            get { return (bool)GetValue(IsMarkdownProperty); }
+            set { SetValue(IsMarkdownProperty, value); }
+        }
+
         public static readonly DependencyProperty CustomContextMenuProperty = DependencyProperty.Register(
             nameof(CustomContextMenu),
             typeof(bool),
@@ -180,6 +192,13 @@ namespace Peek.FilePreviewer.Controls
                 PreviewBrowser.CoreWebView2.Settings.IsScriptEnabled = IsDevFilePreview;
                 PreviewBrowser.CoreWebView2.Settings.IsWebMessageEnabled = false;
 
+                if (IsMarkdown)
+                {
+                    PreviewBrowser.CoreWebView2.Settings.IsScriptEnabled = false;
+                    PreviewBrowser.CoreWebView2.AddWebResourceRequestedFilter("*", CoreWebView2WebResourceContext.All);
+                    PreviewBrowser.CoreWebView2.WebResourceRequested += CoreWebView2_WebResourceRequested;
+                }
+
                 if (IsDevFilePreview)
                 {
                     PreviewBrowser.CoreWebView2.SetVirtualHostNameToFolderMapping(Microsoft.PowerToys.FilePreviewCommon.MonacoHelper.VirtualHostName, Microsoft.PowerToys.FilePreviewCommon.MonacoHelper.MonacoDirectory, CoreWebView2HostResourceAccessKind.Allow);
@@ -201,6 +220,15 @@ namespace Peek.FilePreviewer.Controls
             Navigate();
         }
 
+        private void CoreWebView2_WebResourceRequested(CoreWebView2 sender, CoreWebView2WebResourceRequestedEventArgs args)
+        {
+            // Show local file we've saved with the markdown contents. Block all else.
+            if (Source != null && new Uri(args.Request.Uri) != Source)
+            {
+                args.Response = sender.Environment.CreateWebResourceResponse(null, 403, "Forbidden", null);
+            }
+        }
+
         private List<Control> GetContextMenuItems(CoreWebView2 sender, CoreWebView2ContextMenuRequestedEventArgs args)
         {
             var menuItems = args.MenuItems;

src/modules/peek/Peek.FilePreviewer/FilePreview.xaml

@@ -88,6 +88,7 @@
             DOMContentLoaded="BrowserPreview_DOMContentLoaded"
             FlowDirection="LeftToRight"
             IsDevFilePreview="{x:Bind BrowserPreviewer.IsDevFilePreview, Mode=OneWay}"
+            IsMarkdown="{x:Bind BrowserPreviewer.IsMarkdown, Mode=OneWay}"
             NavigationCompleted="PreviewBrowser_NavigationCompleted"
             Source="{x:Bind BrowserPreviewer.Preview, Mode=OneWay}"
             Visibility="{x:Bind IsPreviewVisible(BrowserPreviewer, Previewer.State), Mode=OneWay, FallbackValue=Collapsed}" />

src/modules/peek/Peek.FilePreviewer/Previewers/Interfaces/IBrowserPreviewer.cs

@@ -12,6 +12,8 @@ namespace Peek.FilePreviewer.Previewers.Interfaces
 
         public bool IsDevFilePreview { get; }
 
+        public bool IsMarkdown { get; }
+
         public bool CustomContextMenu { get; }
     }
 }

src/modules/peek/Peek.FilePreviewer/Previewers/WebBrowserPreviewer/WebBrowserPreviewer.cs

@@ -48,6 +48,9 @@ namespace Peek.FilePreviewer.Previewers
         [ObservableProperty]
         private bool isDevFilePreview;
 
+        [ObservableProperty]
+        private bool isMarkdown;
+
         [ObservableProperty]
         private bool customContextMenu;
 
@@ -122,6 +125,7 @@ namespace Peek.FilePreviewer.Previewers
 
                     IsDevFilePreview = supportedByMonaco;
                     CustomContextMenu = useMonaco;
+                    IsMarkdown = isMarkdown;
 
                     if (useMonaco)
                     {