diff --git a/tests/wpt/mozilla/tests/css/iframe/overflow.html b/tests/wpt/mozilla/tests/css/iframe/overflow.html
index 473f21dc418..d78bad27546 100644
--- a/tests/wpt/mozilla/tests/css/iframe/overflow.html
+++ b/tests/wpt/mozilla/tests/css/iframe/overflow.html
@@ -1,9 +1,14 @@
-<html>
+<html class="reftest-wait">
 <link rel=match href=overflow_ref.html>
  <body>
    <iframe src="data:text/html,%3Cdiv%20style%3D%22background%3Agreen%3B%20width%3A%20200px%3B%20height%3A%20200px%3B%22%3E%3C%2Fdiv%3E"
            style="display: block; width: 108px; height: 108px; border: none">
   </iframe>
+  <script type="text/javascript">
+    window.onload = function() {
+        document.documentElement.classList.remove("reftest-wait");
+    }
+  </script>
  </div>
 </body>
 </html>
diff --git a/tests/wpt/mozilla/tests/css/iframe/positioning_margin.html b/tests/wpt/mozilla/tests/css/iframe/positioning_margin.html
index 57e7a875034..2c6d93c492e 100644
--- a/tests/wpt/mozilla/tests/css/iframe/positioning_margin.html
+++ b/tests/wpt/mozilla/tests/css/iframe/positioning_margin.html
@@ -1,9 +1,14 @@
-<html>
+<html class="reftest-wait">
   <link rel=match href=positioning_margin_ref.html>
   <body style="margin: 0px;">
     <iframe src="data:text/html,%3Chtml%3E%3Cbody%20style%3D%22margin%3A%200px%3B%22%3E%3Cdiv%20style%3D%22background%3A%20green%3B%20height%3A%20100px%3B%20width%3A%20100px%3B%22%3E%3C%2Fdiv%3E%3C%2Fbody%3E%3C%2Fhtml%3E"
         style="display: block; border: 0px; width: 100px; height: 100px; margin-top: 100px;">
     </iframe>
+    <script type="text/javascript">
+      window.onload = function() {
+          document.documentElement.classList.remove("reftest-wait");
+      }
+    </script>
   </body>
 </html>
 
