diff --git a/src/libraries/Microsoft.VisualBasic.Core/tests/Microsoft.VisualBasic.Core.Tests.csproj b/src/libraries/Microsoft.VisualBasic.Core/tests/Microsoft.VisualBasic.Core.Tests.csproj
index 24d99e141ccdc9..83c45050ded286 100644
--- a/src/libraries/Microsoft.VisualBasic.Core/tests/Microsoft.VisualBasic.Core.Tests.csproj
+++ b/src/libraries/Microsoft.VisualBasic.Core/tests/Microsoft.VisualBasic.Core.Tests.csproj
@@ -3,6 +3,12 @@
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(TargetOS)' == 'browser' and '$(WasmEnableThreads)' == 'true'">
+    <WasmXHarnessMaxParallelThreads>1</WasmXHarnessMaxParallelThreads>
+    <XunitShowProgress>true</XunitShowProgress>
+    <!-- VSF is emulated on the UI thread and all calls are slow because they are marshaled -->
+    <WasmXHarnessTestsTimeout>01:15:00</WasmXHarnessTestsTimeout>
+  </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CoreLibSharedDir)System\Runtime\CompilerServices\IsExternalInit.cs" Link="Common\System\Runtime\CompilerServices\IsExternalInit.cs" />
     <Compile Include="AssemblyAttributes.cs" />
diff --git a/src/libraries/System.Private.Xml/tests/System.Private.Xml.Tests.csproj b/src/libraries/System.Private.Xml/tests/System.Private.Xml.Tests.csproj
index d3a6bcda8d572c..7c12f76604c71a 100644
--- a/src/libraries/System.Private.Xml/tests/System.Private.Xml.Tests.csproj
+++ b/src/libraries/System.Private.Xml/tests/System.Private.Xml.Tests.csproj
@@ -17,6 +17,8 @@
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(TargetOS)' == 'browser' and '$(WasmEnableThreads)' == 'true'">
+    <WasmXHarnessMaxParallelThreads>1</WasmXHarnessMaxParallelThreads>
+    <XunitShowProgress>true</XunitShowProgress>
     <!-- VSF is emulated on the UI thread and all calls are slow because they are marshaled -->
     <WasmXHarnessTestsTimeout>01:15:00</WasmXHarnessTestsTimeout>
   </PropertyGroup>
diff --git a/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/System.IO.FileSystem.Tests.csproj b/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/System.IO.FileSystem.Tests.csproj
index 1efe4630f398b1..77100193a31e2a 100644
--- a/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/System.IO.FileSystem.Tests.csproj
+++ b/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/System.IO.FileSystem.Tests.csproj
@@ -7,6 +7,8 @@
     <WasmXHarnessMonoArgs>--working-dir=/test-dir</WasmXHarnessMonoArgs>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetOS)' == 'browser' and '$(WasmEnableThreads)' == 'true'">
+    <WasmXHarnessMaxParallelThreads>1</WasmXHarnessMaxParallelThreads>
+    <XunitShowProgress>true</XunitShowProgress>
     <!-- VSF is emulated on the UI thread and all calls are slow because they are marshaled -->
     <WasmXHarnessTestsTimeout>01:15:00</WasmXHarnessTestsTimeout>
   </PropertyGroup>
diff --git a/src/libraries/System.Runtime/tests/System.IO.Tests/System.IO.Tests.csproj b/src/libraries/System.Runtime/tests/System.IO.Tests/System.IO.Tests.csproj
index c7286f40f1518e..18a73faa56fa62 100644
--- a/src/libraries/System.Runtime/tests/System.IO.Tests/System.IO.Tests.csproj
+++ b/src/libraries/System.Runtime/tests/System.IO.Tests/System.IO.Tests.csproj
@@ -6,6 +6,12 @@
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(TargetOS)' == 'browser' and '$(WasmEnableThreads)' == 'true'">
+    <WasmXHarnessMaxParallelThreads>1</WasmXHarnessMaxParallelThreads>
+    <XunitShowProgress>true</XunitShowProgress>
+    <!-- VSF is emulated on the UI thread and all calls are slow because they are marshaled -->
+    <WasmXHarnessTestsTimeout>01:15:00</WasmXHarnessTestsTimeout>
+  </PropertyGroup>
   <ItemGroup>
     <Compile Include="IndentedTextWriter.cs" />
     <Compile Include="BinaryReader\BinaryReaderTests.cs" />
diff --git a/src/libraries/sendtohelix-browser.targets b/src/libraries/sendtohelix-browser.targets
index 11dcb6fa04d057..dd69df76f31c58 100644
--- a/src/libraries/sendtohelix-browser.targets
+++ b/src/libraries/sendtohelix-browser.targets
@@ -247,6 +247,8 @@
         <!-- VSF is emulated on the UI thread and all calls are slow because they are marshaled -->
         <Timeout Condition="'%(FileName)' == 'System.IO.FileSystem.Tests' and '$(WasmEnableThreads)' == 'true'">01:20:00</Timeout>
         <Timeout Condition="'%(FileName)' == 'System.Private.Xml.Tests' and '$(WasmEnableThreads)' == 'true'">01:20:00</Timeout>
+        <Timeout Condition="'%(FileName)' == 'Microsoft.VisualBasic.Core.Tests' and '$(WasmEnableThreads)' == 'true'">01:20:00</Timeout>
+        <Timeout Condition="'%(FileName)' == 'System.IO.Tests' and '$(WasmEnableThreads)' == 'true'">01:20:00</Timeout>
       </HelixWorkItem>
     </ItemGroup>