--- a/dom/base/nsINode.h
+++ b/dom/base/nsINode.h
@@ -938,16 +938,21 @@ public:
 
   /**
    * Get the root of the subtree this node belongs to.  This never returns
    * null.  It may return 'this' (e.g. for document nodes, and nodes that
    * are the roots of disconnected subtrees).
    */
   nsINode* SubtreeRoot() const;
 
+  nsINode* RootNode() const
+  {
+    return SubtreeRoot();
+  }
+
   /**
    * See nsIDOMEventTarget
    */
   NS_DECL_NSIDOMEVENTTARGET
 
   virtual mozilla::EventListenerManager*
     GetExistingListenerManager() const override;
   virtual mozilla::EventListenerManager*

--- a/dom/webidl/Node.webidl
+++ b/dom/webidl/Node.webidl
@@ -32,16 +32,18 @@ interface Node : EventTarget {
   readonly attribute DOMString nodeName;
 
   [Pure]
   readonly attribute DOMString? baseURI;
 
   [Pure]
   readonly attribute Document? ownerDocument;
   [Pure]
+  readonly attribute Node rootNode;
+  [Pure]
   readonly attribute Node? parentNode;
   [Pure]
   readonly attribute Element? parentElement;
   [Pure]
   boolean hasChildNodes();
   [SameObject]
   readonly attribute NodeList childNodes;
   [Pure]

--- a/testing/web-platform/meta/dom/interfaces.html.ini
+++ b/testing/web-platform/meta/dom/interfaces.html.ini
@@ -286,28 +286,16 @@
     expected: FAIL
 
   [DOMTokenList interface: document.body.classList must inherit property "supports" with the proper type (7)]
     expected: FAIL
 
   [DOMTokenList interface: calling supports(DOMString) on document.body.classList with too few arguments must throw TypeError]
     expected: FAIL
 
-  [Node interface: attribute rootNode]
-    expected: FAIL
-
-  [Node interface: xmlDoc must inherit property "rootNode" with the proper type (16)]
-    expected: FAIL
-
-  [Node interface: document.createDocumentFragment() must inherit property "rootNode" with the proper type (16)]
-    expected: FAIL
-
-  [Node interface: document.doctype must inherit property "rootNode" with the proper type (16)]
-    expected: FAIL
-
   [Element interface: element must inherit property "prepend" with the proper type (32)]
     expected: FAIL
 
   [Element interface: element must inherit property "append" with the proper type (33)]
     expected: FAIL
 
   [Element interface: element must inherit property "query" with the proper type (34)]
     expected: FAIL
@@ -319,20 +307,8 @@
     expected: FAIL
 
   [Element interface: element must inherit property "after" with the proper type (41)]
     expected: FAIL
 
   [Element interface: element must inherit property "replaceWith" with the proper type (42)]
     expected: FAIL
 
-  [Node interface: element must inherit property "rootNode" with the proper type (16)]
-    expected: FAIL
-
-  [Node interface: document.createTextNode("abc") must inherit property "rootNode" with the proper type (16)]
-    expected: FAIL
-
-  [Node interface: xmlDoc.createProcessingInstruction("abc", "def") must inherit property "rootNode" with the proper type (16)]
-    expected: FAIL
-
-  [Node interface: document.createComment("abc") must inherit property "rootNode" with the proper type (16)]
-    expected: FAIL
-

deleted file mode 100644
--- a/testing/web-platform/meta/dom/nodes/rootNode.html.ini
+++ /dev/null
@@ -1,14 +0,0 @@
-[rootNode.html]
-  type: testharness
-  [rootNode attribute must return the context object when it does not have any parent]
-    expected: FAIL
-
-  [rootNode attribute must return the parent node of the context object when the context object has a single ancestor not in a document]
-    expected: FAIL
-
-  [rootNode attribute must return the document when a node is in document]
-    expected: FAIL
-
-  [rootNode attribute must return a document fragment when a node is in the fragment]
-    expected: FAIL
-