diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index 8ecca588469..9f187275bd7 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -87,6 +87,18 @@
             "url": "/_mozilla/css/class-namespaces.html"
           }
         ],
+        "css/flex_nochild.html": [
+          {
+            "path": "css/flex_nochild.html",
+            "references": [
+              [
+                "/_mozilla/css/flex_nochild-ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/flex_nochild.html"
+          }
+        ],
         "css/setpropertypriority.html": [
           {
             "path": "css/setpropertypriority.html",
@@ -884,6 +896,18 @@
           "url": "/_mozilla/css/class-namespaces.html"
         }
       ],
+      "css/flex_nochild.html": [
+        {
+          "path": "css/flex_nochild.html",
+          "references": [
+            [
+              "/_mozilla/css/flex_nochild-ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/flex_nochild.html"
+        }
+      ],
       "css/setpropertypriority.html": [
         {
           "path": "css/setpropertypriority.html",
diff --git a/tests/wpt/mozilla/meta/css/__dir__.ini b/tests/wpt/mozilla/meta/css/__dir__.ini
new file mode 100644
index 00000000000..dfd23294ccc
--- /dev/null
+++ b/tests/wpt/mozilla/meta/css/__dir__.ini
@@ -0,0 +1,2 @@
+prefs: ["layout.flex.enabled:true",
+        "layout.flex-direction.enabled:true"]
diff --git a/tests/wpt/mozilla/tests/css/flex_nochild-ref.html b/tests/wpt/mozilla/tests/css/flex_nochild-ref.html
new file mode 100644
index 00000000000..590bf19772d
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/flex_nochild-ref.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html>
+    <head>
+      <title>flex_nochild</title>
+      <style>
+        body {
+          margin: 0;
+          width: 20px;
+        }
+        div {
+          float: left;
+          width: 10px;
+          height: 10px;
+          background: red;
+        }
+      </style>
+    </head>
+    <body>
+        <div></div>
+        <div></div>
+    </body>
+</html>
+
diff --git a/tests/wpt/mozilla/tests/css/flex_nochild.html b/tests/wpt/mozilla/tests/css/flex_nochild.html
new file mode 100644
index 00000000000..7bab5719de5
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/flex_nochild.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<html>
+    <head>
+      <title>flex_nochild</title>
+      <link rel=match href="flex_nochild-ref.html">
+      <style>
+        body {
+          margin: 0;
+          width: 20px;
+          display: flex;
+        }
+        div {
+          display: flex;
+          width: 10px;
+          height: 10px;
+          background: red;
+        }
+      </style>
+    </head>
+    <body>
+        <div></div>
+        <div></div>
+    </body>
+</html>
