4 files changed, 15 insertions, 4 deletions
diff --git a/dom/base/CustomElementRegistry.cpp b/dom/base/CustomElementRegistry.cpp
index e619ad599..cc6264b03 100644
--- a/dom/base/CustomElementRegistry.cpp
+++ b/dom/base/CustomElementRegistry.cpp
@@ -52,7 +52,7 @@ CustomElementCallback::Call()
       break;
     case nsIDocument::eAttributeChanged:
       static_cast<LifecycleAttributeChangedCallback *>(mCallback.get())->Call(mThisObject,
-        mArgs.name, mArgs.oldValue, mArgs.newValue, rv);
+        mArgs.name, mArgs.oldValue, mArgs.newValue, mArgs.namespaceURI, rv);
       break;
   }
 }
diff --git a/dom/base/CustomElementRegistry.h b/dom/base/CustomElementRegistry.h
index c45f3f70c..b5903f978 100644
--- a/dom/base/CustomElementRegistry.h
+++ b/dom/base/CustomElementRegistry.h
@@ -34,6 +34,7 @@ struct LifecycleCallbackArgs
   nsString name;
   nsString oldValue;
   nsString newValue;
+  nsString namespaceURI;
 };
 
 class CustomElementCallback
diff --git a/dom/base/Element.cpp b/dom/base/Element.cpp
index 81cc41210..247fbe79e 100644
--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -2590,11 +2590,15 @@ Element::SetAttrAndNotify(int32_t aNamespaceID,
   if (ownerDoc && GetCustomElementData()) {
     nsCOMPtr<nsIAtom> oldValueAtom = oldValue->GetAsAtom();
     nsCOMPtr<nsIAtom> newValueAtom = valueForAfterSetAttr.GetAsAtom();
+    nsAutoString ns;
+    nsContentUtils::NameSpaceManager()->GetNameSpaceURI(aNamespaceID, ns);
+
     LifecycleCallbackArgs args = {
       nsDependentAtomString(aName),
       aModType == nsIDOMMutationEvent::ADDITION ?
         NullString() : nsDependentAtomString(oldValueAtom),
-      nsDependentAtomString(newValueAtom)
+      nsDependentAtomString(newValueAtom),
+      (ns.IsEmpty() ? NullString() : ns)
     };
 
     nsContentUtils::EnqueueLifecycleCallback(
@@ -2845,11 +2849,14 @@ Element::UnsetAttr(int32_t aNameSpaceID, nsIAtom* aName,
 
   nsIDocument* ownerDoc = OwnerDoc();
   if (ownerDoc && GetCustomElementData()) {
+    nsAutoString ns;
+    nsContentUtils::NameSpaceManager()->GetNameSpaceURI(aNameSpaceID, ns);
     nsCOMPtr<nsIAtom> oldValueAtom = oldValue.GetAsAtom();
     LifecycleCallbackArgs args = {
       nsDependentAtomString(aName),
       nsDependentAtomString(oldValueAtom),
-      NullString()
+      NullString(),
+      (ns.IsEmpty() ? NullString() : ns)
     };
 
     nsContentUtils::EnqueueLifecycleCallback(
diff --git a/dom/webidl/WebComponents.webidl b/dom/webidl/WebComponents.webidl
index 3dfb960bc..19ca38c0d 100644
--- a/dom/webidl/WebComponents.webidl
+++ b/dom/webidl/WebComponents.webidl
@@ -13,7 +13,10 @@
 callback LifecycleCreatedCallback = void();
 callback LifecycleAttachedCallback = void();
 callback LifecycleDetachedCallback = void();
-callback LifecycleAttributeChangedCallback = void(DOMString attrName, DOMString? oldValue, DOMString? newValue);
+callback LifecycleAttributeChangedCallback = void(DOMString attrName,
+                                                  DOMString? oldValue,
+                                                  DOMString? newValue,
+                                                  DOMString? namespaceURI);
 
 dictionary LifecycleCallbacks {
   LifecycleCreatedCallback? createdCallback;