diff --git a/core/modules/field_ui/tests/src/FunctionalJavascript/ManageFieldsTest.php b/core/modules/field_ui/tests/src/FunctionalJavascript/ManageFieldsTest.php
index 36fca849dc6f89491e92db9c8623ecc3cafbaf42..53dc85e03eb4ec3aa4532edd1f836bc351fffcc4 100644
--- a/core/modules/field_ui/tests/src/FunctionalJavascript/ManageFieldsTest.php
+++ b/core/modules/field_ui/tests/src/FunctionalJavascript/ManageFieldsTest.php
@@ -15,6 +15,7 @@
  * Tests the Field UI "Manage Fields" screens.
  *
  * @group field_ui
+ * @group #slow
  */
 class ManageFieldsTest extends WebDriverTestBase {
 
diff --git a/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetClaroThemeTest.php b/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetClaroThemeTest.php
index f8c6e315d22be832b3222d438f6f611238398b92..8089031020609f8ca086c8064f7f0b280c904ea3 100644
--- a/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetClaroThemeTest.php
+++ b/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetClaroThemeTest.php
@@ -15,6 +15,7 @@
  * @see _claro_preprocess_file_and_image_widget()
  *
  * @group file
+ * @group #slow
  */
 class FileFieldWidgetClaroThemeTest extends FileFieldWidgetTest {
 
diff --git a/core/modules/rest/tests/src/Functional/ResourceTest.php b/core/modules/rest/tests/src/Functional/ResourceTest.php
index 23e7fa5fb1a919aee24ed7eaf15cbff49e4879fc..64ec7ed09bdf431514ce26c1ba6f63456d1c3318 100644
--- a/core/modules/rest/tests/src/Functional/ResourceTest.php
+++ b/core/modules/rest/tests/src/Functional/ResourceTest.php
@@ -15,6 +15,7 @@
  * Tests the structure of a REST resource.
  *
  * @group rest
+ * @group #slow
  */
 class ResourceTest extends BrowserTestBase {
 
diff --git a/core/modules/system/tests/src/Functional/Form/StorageTest.php b/core/modules/system/tests/src/Functional/Form/StorageTest.php
index 2d3199f48e8bd16efccae4b981bf9efc330cdd08..57f3e286447f9f453d8c0977174cd9a1dceb7ada 100644
--- a/core/modules/system/tests/src/Functional/Form/StorageTest.php
+++ b/core/modules/system/tests/src/Functional/Form/StorageTest.php
@@ -16,6 +16,7 @@
  * values are not lost due to a wrong form rebuild.
  *
  * @group Form
+ * @group #slow
  */
 class StorageTest extends BrowserTestBase {
 
diff --git a/core/modules/system/tests/src/Functional/Form/ValidationTest.php b/core/modules/system/tests/src/Functional/Form/ValidationTest.php
index 328fca30be0affd8c6d56af64a69ee77bba5eaf9..4d28dd997e4b6b08516ae189a3d5a7bbb749623c 100644
--- a/core/modules/system/tests/src/Functional/Form/ValidationTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ValidationTest.php
@@ -9,6 +9,7 @@
  * Tests form processing and alteration via form validation handlers.
  *
  * @group Form
+ * @group #slow
  */
 class ValidationTest extends BrowserTestBase {
 
diff --git a/core/modules/system/tests/src/FunctionalJavascript/ModuleFilterTest.php b/core/modules/system/tests/src/FunctionalJavascript/ModuleFilterTest.php
index 02115807ddd85e489a95e86f9526ecf79b26dc3f..308fa70a84c9417757561c98894e18ac04c11c7e 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/ModuleFilterTest.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/ModuleFilterTest.php
@@ -10,6 +10,7 @@
  * Tests the JavaScript functionality of the module filter.
  *
  * @group system
+ * @group #slow
  */
 class ModuleFilterTest extends WebDriverTestBase {
 
diff --git a/core/modules/views_ui/tests/src/Functional/OverrideDisplaysTest.php b/core/modules/views_ui/tests/src/Functional/OverrideDisplaysTest.php
index 2dac1a7d1c2a9d405243569eac00178d71a8a475..8208210e051a6553eb6150e5788e4d01857ef576 100644
--- a/core/modules/views_ui/tests/src/Functional/OverrideDisplaysTest.php
+++ b/core/modules/views_ui/tests/src/Functional/OverrideDisplaysTest.php
@@ -6,6 +6,7 @@
  * Tests that displays can be correctly overridden via the user interface.
  *
  * @group views_ui
+ * @group #slow
  */
 class OverrideDisplaysTest extends UITestBase {
 
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/MachineName/MachineNameTransliterationTest.php b/core/tests/Drupal/FunctionalJavascriptTests/MachineName/MachineNameTransliterationTest.php
index 8a6c37db1aed2b4e6bb038126d1850e0c02507a3..d223feab7b5a8d377314f771068e95794f73f2e6 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/MachineName/MachineNameTransliterationTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/MachineName/MachineNameTransliterationTest.php
@@ -12,6 +12,7 @@
  * Tests the machine name transliteration functionality.
  *
  * @group javascript
+ * @group #slow
  */
 class MachineNameTransliterationTest extends WebDriverTestBase {