diff --git a/tests/ref/basic.list b/tests/ref/basic.list
index 7974f260f49..c70666af324 100644
--- a/tests/ref/basic.list
+++ b/tests/ref/basic.list
@@ -349,7 +349,6 @@ resolution=300x300,device-pixel-ratio=2 != pixel_snapping_position_a.html pixel_
== transform_skew_a.html transform_skew_ref.html
== transform_stacking_context_a.html transform_stacking_context_ref.html
== transition_calc.html transition_calc_ref.html
-== upper_id_attr.html upper_id_attr_ref.html
flaky_cpu,prefs:"layout.writing-mode.enabled" == vertical-lr-blocks.html vertical-lr-blocks_ref.html
== vertical_align_bottom_a.html vertical_align_bottom_ref.html
== vertical_align_inline_block_a.html vertical_align_inline_block_ref.html
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index 53d2473d6d1..0ba0b2ff4a4 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -603,6 +603,18 @@
"url": "/_mozilla/css/stacking_context_rtl.html"
}
],
+ "css/upper_id_attr.html": [
+ {
+ "path": "css/upper_id_attr.html",
+ "references": [
+ [
+ "/_mozilla/css/upper_id_attr_ref.html",
+ "=="
+ ]
+ ],
+ "url": "/_mozilla/css/upper_id_attr.html"
+ }
+ ],
"css/vertical_align_text_top_a.html": [
{
"path": "css/vertical_align_text_top_a.html",
@@ -2000,6 +2012,18 @@
"url": "/_mozilla/css/stacking_context_rtl.html"
}
],
+ "css/upper_id_attr.html": [
+ {
+ "path": "css/upper_id_attr.html",
+ "references": [
+ [
+ "/_mozilla/css/upper_id_attr_ref.html",
+ "=="
+ ]
+ ],
+ "url": "/_mozilla/css/upper_id_attr.html"
+ }
+ ],
"css/vertical_align_text_top_a.html": [
{
"path": "css/vertical_align_text_top_a.html",
diff --git a/tests/ref/upper_id_attr.html b/tests/wpt/mozilla/tests/css/upper_id_attr.html
similarity index 79%
rename from tests/ref/upper_id_attr.html
rename to tests/wpt/mozilla/tests/css/upper_id_attr.html
index 0f6c20f6391..58052e02259 100644
--- a/tests/ref/upper_id_attr.html
+++ b/tests/wpt/mozilla/tests/css/upper_id_attr.html
@@ -1,4 +1,5 @@
+