diff --git a/src/libraries/Common/tests/TestUtilities/System/PlatformDetection.Unix.cs b/src/libraries/Common/tests/TestUtilities/System/PlatformDetection.Unix.cs
index a4a74cdc9ee4af..a042993849156e 100644
--- a/src/libraries/Common/tests/TestUtilities/System/PlatformDetection.Unix.cs
+++ b/src/libraries/Common/tests/TestUtilities/System/PlatformDetection.Unix.cs
@@ -47,9 +47,9 @@ public static partial class PlatformDetection
         public static bool IsNotFedoraOrRedHatFamily => !IsFedora && !IsRedHatFamily;
         public static bool IsNotDebian10 => !IsDebian10;
 
-        public static bool IsSuperUser => !IsWindows ?
+        public static bool IsSuperUser => IsBrowser ? false : (!IsWindows ?
             libc.geteuid() == 0 :
-            throw new PlatformNotSupportedException();
+            throw new PlatformNotSupportedException());
 
         public static Version OpenSslVersion => !IsOSXLike && !IsWindows ?
             GetOpenSslVersion() :
diff --git a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFile.CreateFromFile.Tests.cs b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFile.CreateFromFile.Tests.cs
index 548bcbc323648b..d5edbbc05b2944 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFile.CreateFromFile.Tests.cs
+++ b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFile.CreateFromFile.Tests.cs
@@ -614,6 +614,7 @@ public void FileInUse_CreateFromFile_FailsWithExistingReadWriteMap()
         /// Test exceptional behavior when trying to create a map for a non-shared file that's currently in use.
         /// </summary>
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // the emscripten implementation ignores FileShare.None
         public void FileInUse_CreateFromFile_FailsWithExistingNoShareFile()
         {
             // Already opened with a FileStream
@@ -696,13 +697,13 @@ private void WriteToReadOnlyFile(MemoryMappedFileAccess access, bool succeeds)
         public void WriteToReadOnlyFile_ReadWrite(MemoryMappedFileAccess access)
         {
             WriteToReadOnlyFile(access, access == MemoryMappedFileAccess.Read ||
-                            (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) && geteuid() == 0));
+                            (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) && PlatformDetection.IsSuperUser));
         }
 
         [Fact]
         public void WriteToReadOnlyFile_CopyOnWrite()
         {
-            WriteToReadOnlyFile(MemoryMappedFileAccess.CopyOnWrite, (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) && geteuid() == 0));
+            WriteToReadOnlyFile(MemoryMappedFileAccess.CopyOnWrite, (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) && PlatformDetection.IsSuperUser));
         }
 
         /// <summary>
@@ -768,6 +769,7 @@ public void LeaveOpenRespected_OutstandingViews(bool leaveOpen)
         /// Test to validate we can create multiple maps from the same FileStream.
         /// </summary>
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // the emscripten implementation doesn't share data
         public void MultipleMapsForTheSameFileStream()
         {
             const int Capacity = 4096;
diff --git a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFilesTestsBase.Unix.cs b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFilesTestsBase.Unix.cs
index 6b1042ae1e4e34..c754fcb8daaf15 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFilesTestsBase.Unix.cs
+++ b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFilesTestsBase.Unix.cs
@@ -14,6 +14,9 @@ public abstract partial class MemoryMappedFilesTestBase : FileCleanupTestBase
         /// <summary>Gets the system's page size.</summary>
         protected static Lazy<int> s_pageSize = new Lazy<int>(() =>
         {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Browser))
+                return Environment.SystemPageSize;
+
             int pageSize;
             const int _SC_PAGESIZE_FreeBSD = 47;
             const int _SC_PAGESIZE_Linux = 30;
@@ -31,9 +34,6 @@ public abstract partial class MemoryMappedFilesTestBase : FileCleanupTestBase
         [DllImport("libc", SetLastError = true)]
         private static extern int sysconf(int name);
 
-        [DllImport("libc", SetLastError = true)]
-        protected static extern int geteuid();
-
         /// <summary>Asserts that the handle's inheritability matches the specified value.</summary>
         protected static void AssertInheritability(SafeHandle handle, HandleInheritability inheritability)
         {
diff --git a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewAccessor.Tests.cs b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewAccessor.Tests.cs
index 99268f6f7d8429..f96e00479ae3e1 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewAccessor.Tests.cs
+++ b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewAccessor.Tests.cs
@@ -334,6 +334,7 @@ public void FlushSupportedOnBothReadAndWriteAccessors(MemoryMappedFileAccess acc
         /// Test to validate that multiple accessors over the same map share data appropriately.
         /// </summary>
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // the emscripten implementation doesn't share data
         public void ViewsShareData()
         {
             const int MapLength = 256;
diff --git a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewStream.Tests.cs b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewStream.Tests.cs
index a4ab65c1263667..5f98409f3fe2f8 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewStream.Tests.cs
+++ b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewStream.Tests.cs
@@ -264,6 +264,7 @@ public void FlushSupportedOnBothReadAndWriteAccessors(MemoryMappedFileAccess acc
         /// Test to validate that multiple accessors over the same map share data appropriately.
         /// </summary>
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // the emscripten implementation doesn't share data
         public void ViewsShareData()
         {
             const int MapLength = 256;
diff --git a/src/libraries/tests.proj b/src/libraries/tests.proj
index d6dd69b9138cce..d871351d197163 100644
--- a/src/libraries/tests.proj
+++ b/src/libraries/tests.proj
@@ -32,7 +32,6 @@
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Globalization.Extensions\tests\System.Globalization.Extensions.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Globalization\tests\System.Globalization.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.IO.FileSystem\tests\System.IO.FileSystem.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.IO.MemoryMappedFiles\tests\System.IO.MemoryMappedFiles.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.IO.Packaging\tests\System.IO.Packaging.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Linq.Expressions\tests\System.Linq.Expressions.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Linq.Parallel\tests\System.Linq.Parallel.Tests.csproj" />