diff --git a/tests/ref/basic.list b/tests/ref/basic.list
index 9b30eea754f..2b919662b54 100644
--- a/tests/ref/basic.list
+++ b/tests/ref/basic.list
@@ -4,9 +4,6 @@
 # Should be == with expected failure:
 fragment=top != ../html/acid2.html acid2_ref.html
 
-flaky_cpu == append_style_a.html append_style_b.html
-# `?` and `#` in the name is a test for https://github.com/servo/servo/issues/3340
-
 resolution=300x300,device-pixel-ratio=2 != pixel_snapping_border_a.html pixel_snapping_border_ref.html
 resolution=300x300,device-pixel-ratio=2 != pixel_snapping_position_a.html pixel_snapping_position_ref.html
 resolution=800x600 == viewport_percentage_vmin_vmax.html viewport_percentage_vmin_vmax_a.html
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index ae7c3f4e3ba..153acb28867 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -211,6 +211,18 @@
             "url": "/_mozilla/css/anon_block_inherit_a.html"
           }
         ],
+        "css/append_style_a.html": [
+          {
+            "path": "css/append_style_a.html",
+            "references": [
+              [
+                "/_mozilla/css/append_style_b.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/append_style_a.html"
+          }
+        ],
         "css/attr_exists_selector.html": [
           {
             "path": "css/attr_exists_selector.html",
@@ -6054,6 +6066,18 @@
           "url": "/_mozilla/css/anon_block_inherit_a.html"
         }
       ],
+      "css/append_style_a.html": [
+        {
+          "path": "css/append_style_a.html",
+          "references": [
+            [
+              "/_mozilla/css/append_style_b.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/append_style_a.html"
+        }
+      ],
       "css/attr_exists_selector.html": [
         {
           "path": "css/attr_exists_selector.html",
diff --git a/tests/ref/append_style_a.html b/tests/wpt/mozilla/tests/css/append_style_a.html
similarity index 62%
rename from tests/ref/append_style_a.html
rename to tests/wpt/mozilla/tests/css/append_style_a.html
index 40521ba3d08..3856eb98f47 100644
--- a/tests/ref/append_style_a.html
+++ b/tests/wpt/mozilla/tests/css/append_style_a.html
@@ -1 +1,2 @@
+<link rel=match href=append_style_b.html>
 <div style="background-color: blue">this is the story of a girl</div>
diff --git a/tests/ref/append_style_b.html b/tests/wpt/mozilla/tests/css/append_style_b.html
similarity index 100%
rename from tests/ref/append_style_b.html
rename to tests/wpt/mozilla/tests/css/append_style_b.html