diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index ee90a1be5d4..81cf142111f 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -2496,6 +2496,18 @@
             "url": "/_mozilla/css/inline_block_min_width.html"
           }
         ],
+        "css/inline_block_opacity_change.html": [
+          {
+            "path": "css/inline_block_opacity_change.html",
+            "references": [
+              [
+                "/_mozilla/css/inline_block_opacity_change_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/inline_block_opacity_change.html"
+          }
+        ],
         "css/inline_block_overflow.html": [
           {
             "path": "css/inline_block_overflow.html",
@@ -11764,6 +11776,18 @@
           "url": "/_mozilla/css/inline_block_min_width.html"
         }
       ],
+      "css/inline_block_opacity_change.html": [
+        {
+          "path": "css/inline_block_opacity_change.html",
+          "references": [
+            [
+              "/_mozilla/css/inline_block_opacity_change_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/inline_block_opacity_change.html"
+        }
+      ],
       "css/inline_block_overflow.html": [
         {
           "path": "css/inline_block_overflow.html",
diff --git a/tests/wpt/mozilla/tests/css/inline_block_opacity_change.html b/tests/wpt/mozilla/tests/css/inline_block_opacity_change.html
new file mode 100644
index 00000000000..aa51ab444cd
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/inline_block_opacity_change.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <link rel="match" href="inline_block_opacity_change_ref.html">
+    <style>
+    #a {
+        background-color: green;
+        display: inline-block;
+        width: 1em;
+        opacity: 0.2;
+    }
+
+    #a.go {
+        opacity: 1;
+    }
+    </style>
+</head>
+
+<body>
+    <span style="transition: opacity .1s ease-out;" id="a">a</span>
+    <script>
+            document.body.offsetWidth; // force layout
+            document.querySelector('#a').classList.add('go');
+    </script>
+</body>
+</html>
diff --git a/tests/wpt/mozilla/tests/css/inline_block_opacity_change_ref.html b/tests/wpt/mozilla/tests/css/inline_block_opacity_change_ref.html
new file mode 100644
index 00000000000..d047a3a8517
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/inline_block_opacity_change_ref.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <style>
+    #a {
+        background-color: green;
+        display: inline-block;
+        width: 1em;
+        opacity: 1;
+    }
+    </style>
+</head>
+
+<body>
+    <span id="a">a</span>
+</body>
+</html>
