Add Edge WebView2 as an alternative.

WebView2 is the default. To use old set useOldViewer to true in config file.
WebView2 will also preview svg, txt and pdf files.

QuickLook.Plugin/QuickLook.Plugin.HtmlViewer/BrowserPanel.xaml

@@ -0,0 +1,18 @@
+<UserControl x:Class="QuickLook.Plugin.HtmlViewer.BrowserPanel"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
+             xmlns:wv2="clr-namespace:Microsoft.Web.WebView2.Wpf;assembly=Microsoft.Web.WebView2.Wpf"        
+             xmlns:local="clr-namespace:QuickLook.Plugin.HtmlViewer"
+             mc:Ignorable="d" 
+             d:DesignHeight="450" d:DesignWidth="800">
+    <UserControl.Resources>
+        <wv2:CoreWebView2CreationProperties x:Key="EvergreenWebView2CreationProperties" />
+    </UserControl.Resources>
+    <wv2:WebView2
+        x:Name="webView"
+        CreationProperties="{StaticResource EvergreenWebView2CreationProperties}"
+        NavigationStarting="NavigationStarting"
+    />
+</UserControl>

QuickLook.Plugin/QuickLook.Plugin.HtmlViewer/BrowserPanel.xaml.cs

@@ -0,0 +1,59 @@
+using Microsoft.Web.WebView2.Core;
+using System;
+using System.IO;
+using System.Windows.Controls;
+
+namespace QuickLook.Plugin.HtmlViewer
+{
+    /// <summary>
+    /// Interaction logic for BrowserPanel.xaml
+    /// </summary>
+    public partial class BrowserPanel : UserControl
+    {
+        private Uri _currentUri;
+
+        public BrowserPanel()
+        {
+            InitializeComponent();
+        }
+
+        public void LoadFile(string path)
+        {
+            if (Path.IsPathRooted(path))
+                path = Helper.FilePathToFileUrl(path);  
+
+            Navigate(path);
+        }
+
+        public void Navigate(string uri)
+        {
+            if (!string.IsNullOrWhiteSpace(uri) && Uri.IsWellFormedUriString(uri, UriKind.Absolute))
+                try
+                {
+                    webView.Source = new Uri(uri);
+                }
+                catch (UriFormatException)
+                {
+                    // just don't crash because of a malformed url
+                }
+            else
+                webView.Source = null;
+
+            _currentUri = webView.Source;
+        }
+
+        public void Dispose()
+        {
+            webView.Dispose();
+        }
+
+        void NavigationStarting(object sender, CoreWebView2NavigationStartingEventArgs e)
+        {
+            var newUri = new Uri(e.Uri);
+            if (newUri != _currentUri)
+            {
+                e.Cancel = true;
+            }
+        }
+    }
+}

QuickLook.Plugin/QuickLook.Plugin.HtmlViewer/Plugin.cs

@@ -21,17 +21,61 @@
 using System.Windows;
 using System.Windows.Threading;
 using QuickLook.Common.Plugin;
+using QuickLook.Common.Helpers;
 
 namespace QuickLook.Plugin.HtmlViewer
 {
-    public class Plugin : IViewer
+    internal class WebviewPluginImpl : IViewer
     {
-        private static readonly string[] Extensions = { ".mht", ".mhtml", ".htm", ".html" };
+        public int Priority => 0;
+        private static readonly string[] Extensions = { ".mht", ".mhtml", ".htm", ".html", ".svg", ".txt", ".pdf" };
         private static readonly string[] SupportedProtocols = { "http", "https" };
 
-        private WebpagePanel _panel;
+        private BrowserPanel _panel;
+
+        public void Init()
+        {
+        }
+
+        public bool CanHandle(string path)
+        {
+            return !Directory.Exists(path) && (Extensions.Any(path.ToLower().EndsWith) || (path.ToLower().EndsWith(".url") && SupportedProtocols.Contains(Helper.GetUrlPath(path).Split(':')[0].ToLower())));
+        }
+
+        public void Prepare(string path, ContextObject context)
+        {
+            var desiredSize = new Size(1200, 1600);
+            context.SetPreferredSizeFit(desiredSize, 0.8);
+        }
+
+        public void View(string path, ContextObject context)
+        {
+            _panel = new BrowserPanel();
+            context.ViewerContent = _panel;
+            context.Title = Path.IsPathRooted(path) ? Path.GetFileName(path) : path;
+
+            if (path.ToLower().EndsWith(".url"))
+            {
+                path = Helper.GetUrlPath(path);
+            }
+            _panel.LoadFile(path);
+            _panel.Dispatcher.Invoke(() => { context.IsBusy = false; }, DispatcherPriority.Loaded);
+        }
+
+        public void Cleanup()
+        {
+            _panel?.Dispose();
+            _panel = null;
+        }
 
+    }
+    internal class OldWebpagePluginImpl : IViewer
+    {
         public int Priority => 0;
+        private static readonly string[] Extensions = { ".mht", ".mhtml", ".htm", ".html" };
+        private static readonly string[] SupportedProtocols = { "http", "https" };
+
+        private WebpagePanel _panel;
 
         public void Init()
         {
@@ -68,4 +112,44 @@ public void Cleanup()
             _panel = null;
         }
     }
+    public class Plugin : IViewer
+    {
+        public int Priority => 0;
+        private static IViewer _impl;
+
+        public void Init()
+        {
+            var useOldViewer = SettingHelper.Get("useOldViewer", false);
+            if (useOldViewer)
+            {
+                _impl = new OldWebpagePluginImpl();
+            } 
+            else
+            {
+                _impl = new WebviewPluginImpl();
+
+            }
+            _impl.Init();
+        }
+
+        public bool CanHandle(string path)
+        {
+            return _impl.CanHandle(path);
+        }
+
+        public void Prepare(string path, ContextObject context)
+        {
+            _impl.Prepare(path, context);
+        }
+
+        public void View(string path, ContextObject context)
+        {
+            _impl.View(path, context);
+        }
+
+        public void Cleanup()
+        {
+            _impl.Cleanup();
+        }
+    }
 }

QuickLook.Plugin/QuickLook.Plugin.HtmlViewer/QuickLook.Plugin.HtmlViewer.csproj

@@ -61,6 +61,15 @@
   </PropertyGroup>
   <ItemGroup>
     <Reference Include="Microsoft.CSharp" />
+    <Reference Include="Microsoft.Web.WebView2.Core, Version=1.0.664.37, Culture=neutral, PublicKeyToken=2a8ab48044d2601e, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Microsoft.Web.WebView2.1.0.664.37\lib\net462\Microsoft.Web.WebView2.Core.dll</HintPath>
+    </Reference>
+    <Reference Include="Microsoft.Web.WebView2.WinForms, Version=1.0.664.37, Culture=neutral, PublicKeyToken=2a8ab48044d2601e, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Microsoft.Web.WebView2.1.0.664.37\lib\net462\Microsoft.Web.WebView2.WinForms.dll</HintPath>
+    </Reference>
+    <Reference Include="Microsoft.Web.WebView2.Wpf, Version=1.0.664.37, Culture=neutral, PublicKeyToken=2a8ab48044d2601e, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Microsoft.Web.WebView2.1.0.664.37\lib\net462\Microsoft.Web.WebView2.Wpf.dll</HintPath>
+    </Reference>
     <Reference Include="System" />
     <Reference Include="System.Core" />
     <Reference Include="System.Windows.Forms" />
@@ -72,6 +81,9 @@
     <Reference Include="PresentationFramework" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="BrowserPanel.xaml.cs">
+      <DependentUpon>BrowserPanel.xaml</DependentUpon>
+    </Compile>
     <Compile Include="WebpagePanel.cs" />
     <Compile Include="WpfBrowserWrapper.cs" />
     <Compile Include="..\..\GitVersion.cs">
@@ -108,5 +120,21 @@
       <EmbedInteropTypes>True</EmbedInteropTypes>
     </COMReference>
   </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
+  <ItemGroup>
+    <Page Include="BrowserPanel.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
+  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <Import Project="..\..\packages\Microsoft.Web.WebView2.1.0.664.37\build\Microsoft.Web.WebView2.targets" Condition="Exists('..\..\packages\Microsoft.Web.WebView2.1.0.664.37\build\Microsoft.Web.WebView2.targets')" />
+  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
+    <PropertyGroup>
+      <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
+    </PropertyGroup>
+    <Error Condition="!Exists('..\..\packages\Microsoft.Web.WebView2.1.0.664.37\build\Microsoft.Web.WebView2.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\..\packages\Microsoft.Web.WebView2.1.0.664.37\build\Microsoft.Web.WebView2.targets'))" />
+  </Target>
 </Project>

QuickLook.Plugin/QuickLook.Plugin.HtmlViewer/packages.config

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="Microsoft.Web.WebView2" version="1.0.664.37" targetFramework="net462" />
+</packages>