diff --git a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-006.html b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-006.html
index 904e7d3fed8c..e4f3f711421c 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-006.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-006.html
@@ -75,5 +75,8 @@
       </math>
     </p>
 
+   <script src="/mathml/support/feature-detection.js"></script>
+   <script>MathMLFeatureDetection.ensure_for_match_reftest("has_dir");</script>
+
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-007.html b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-007.html
index 7137e2640fa4..97dec11b6c62 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-007.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-007.html
@@ -46,5 +46,8 @@
       </math>
     </p>
 
+   <script src="/mathml/support/feature-detection.js"></script>
+   <script>MathMLFeatureDetection.ensure_for_match_reftest("has_dir");</script>
+
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-008.html b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-008.html
index 5c98b0741007..d94a036be00f 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-008.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-008.html
@@ -29,5 +29,8 @@
       </math>
     </p>
 
+   <script src="/mathml/support/feature-detection.js"></script>
+   <script>MathMLFeatureDetection.ensure_for_match_reftest("has_dir");</script>
+
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-009.html b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-009.html
index bf8caf16aed2..c0ca31d40a82 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-009.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-009.html
@@ -23,5 +23,8 @@
       </math>
     </p>
 
+   <script src="/mathml/support/feature-detection.js"></script>
+   <script>MathMLFeatureDetection.ensure_for_match_reftest("has_dir");</script>
+
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-010.html b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-010.html
index 6dc095ac1fd4..4087630e4c99 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/direction/direction-010.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/direction/direction-010.html
@@ -47,5 +47,8 @@
       </math>
     </p>
 
+   <script src="/mathml/support/feature-detection.js"></script>
+   <script>MathMLFeatureDetection.ensure_for_match_reftest("has_dir");</script>
+
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/fractions/frac-rendering-from-in-flow-ref.html b/testing/web-platform/tests/mathml/presentation-markup/fractions/frac-rendering-from-in-flow-ref.html
index 1934bf4969ad..71f1583fd9f1 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/fractions/frac-rendering-from-in-flow-ref.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/fractions/frac-rendering-from-in-flow-ref.html
@@ -10,5 +10,6 @@
         <mspace width="64px" height="48px" style="background: lightblue"></mspace>
         <mspace width="128px" height="96px" style="background: lightgreen"></mspace>
       </mfrac>
+    </math>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/fractions/frac-rendering-from-in-flow.html b/testing/web-platform/tests/mathml/presentation-markup/fractions/frac-rendering-from-in-flow.html
index 8c92d665c738..ac9576ffc4c1 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/fractions/frac-rendering-from-in-flow.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/fractions/frac-rendering-from-in-flow.html
@@ -33,5 +33,8 @@
         <mspace height="16px" width="12px" class="oof2"/>
         <mspace height="8px" width="4px" class="nobox"/>
       </mfrac>
+    </math>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_mfrac");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-dynamic.html b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-dynamic.html
index fff3bd9ff336..72d6c67f7544 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-dynamic.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-dynamic.html
@@ -45,5 +45,7 @@
     _<math><msqrt><mi id="x5">x</mi><mo>−</mo><mi>y</mi></msqrt></math>_
     _<math><mstyle><mi id="x6">x</mi><mo>−</mo><mi>y</mi></mstyle></math>_
 
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_operator_spacing");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-fallback.html b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-fallback.html
index b517dd574688..2c3f3a42765f 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-fallback.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-fallback.html
@@ -22,5 +22,7 @@
       <mo>(</mo> <mspace height="3em" depth="3em"/> <mo>)</mo>
     </math>
 
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-minus-plus.html b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-minus-plus.html
index 487bca25eaa6..06e75429cdd6 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-minus-plus.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form-minus-plus.html
@@ -83,5 +83,7 @@
     _<math><msqrt><mi>x</mi><mo>∓</mo><mi>y</mi></msqrt></math>_
     _<math><mstyle><mi>x</mi><mo>∓</mo><mi>y</mi></mstyle></math>_
 
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_operator_spacing");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form.html b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form.html
index 4f651d1c9b7c..b67b389ec1c4 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-form.html
@@ -24,5 +24,7 @@
     _<math><mo form="prefix">♭</mo></math>_
     _<math><mo form="postfix">♭</mo></math>_
 
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_operator_spacing");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-default.html b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-default.html
index a05bef47ee76..503a57f25c72 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-default.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-default.html
@@ -18,5 +18,7 @@
         <mi>x</mi>
       </munder>
     </math>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-dynamic.html b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-dynamic.html
index 53cf76c0588f..33fe97a3fb31 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-dynamic.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-dynamic.html
@@ -21,5 +21,7 @@
         <mi>x</mi>
       </munder>
     </math>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");</script>
     </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-from-in-flow.html b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-from-in-flow.html
index d50cac50de37..b4f0326481e9 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-from-in-flow.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits-from-in-flow.html
@@ -47,5 +47,7 @@
         <mn>2</mn>
       </munderover>
     </math>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits.html b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits.html
index ebb5cde6f138..82709e42dbfa 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-movablelimits.html
@@ -28,5 +28,7 @@
         <mi>B</mi>
       </munder>
     </math>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-paint-lspace-rspace.html b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-paint-lspace-rspace.html
index 8fb095b61240..0c387f565650 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/operators/mo-paint-lspace-rspace.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/operators/mo-paint-lspace-rspace.html
@@ -65,5 +65,7 @@
       <mo lspace="200px" rspace="100px">→</mo>
       <mspace width="100px" height="10px" depth="10px" style="background: black"></mspace>
     </math>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_operator_spacing");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/radicals/radical-rendering-from-in-flow-ref.html b/testing/web-platform/tests/mathml/presentation-markup/radicals/radical-rendering-from-in-flow-ref.html
index 403a76f483e4..e1b8c3d16107 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/radicals/radical-rendering-from-in-flow-ref.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/radicals/radical-rendering-from-in-flow-ref.html
@@ -13,5 +13,6 @@
         <mspace width="64px" height="12px" style="background: lightblue"></mspace>
         <mspace width="128px" height="24px" style="background: lightgreen"></mspace>
       </mroot>
+    </math>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/radicals/radical-rendering-from-in-flow.html b/testing/web-platform/tests/mathml/presentation-markup/radicals/radical-rendering-from-in-flow.html
index c49a899a0faa..44e449e8fddc 100644
--- a/testing/web-platform/tests/mathml/presentation-markup/radicals/radical-rendering-from-in-flow.html
+++ b/testing/web-platform/tests/mathml/presentation-markup/radicals/radical-rendering-from-in-flow.html
@@ -42,5 +42,8 @@
         <mspace width="16px" class="oof2"/>
         <mspace width="8px" class="nobox"/>
       </mroot>
+    </math>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>MathMLFeatureDetection.ensure_for_match_reftest("has_msqrt");</script>
   </body>
 </html>
diff --git a/testing/web-platform/tests/mathml/support/feature-detection.js b/testing/web-platform/tests/mathml/support/feature-detection.js
index 50ca926d25ea..bdf4d42badfa 100644
--- a/testing/web-platform/tests/mathml/support/feature-detection.js
+++ b/testing/web-platform/tests/mathml/support/feature-detection.js
@@ -119,6 +119,32 @@ var MathMLFeatureDetection = {
         return this._has_menclose;
     },
 
+    has_munderover: function() {
+        if (!this.hasOwnProperty("_has_munderover")) {
+            document.body.insertAdjacentHTML("beforeend", "<math>\
+<munderover>\
+  <mspace width='20px'></mspace>\
+  <mspace width='20px'></mspace>\
+  <mspace width='20px'></mspace>\
+</munderover>\
+<munderover>\
+  <mspace width='40px'></mspace>\
+  <mspace width='40px'></mspace>\
+  <mspace width='40px'></mspace>\
+</munderover>\
+</math>");
+            var math = document.body.lastElementChild;
+            var munderover = math.getElementsByTagName("munderover");
+            // width_delta will be 20px per MathML, 3 * 20 = 60px if mundeover does not stack its children and 0px if mspace is not supported.
+            var width_delta =
+                munderover[1].getBoundingClientRect().width -
+                munderover[0].getBoundingClientRect().width;
+            this._has_munderover = width_delta > 10 && width_delta < 30;
+            document.body.removeChild(math);
+        }
+        return this._has_munderover;
+    },
+
     has_dir: function() {
         if (!this.hasOwnProperty("_has_dir")) {
             document.body.insertAdjacentHTML("beforeend", "<math style='direction: ltr !important;'>\