--- a/dom/base/CustomElementRegistry.cpp
+++ b/dom/base/CustomElementRegistry.cpp
@@ -13,16 +13,67 @@
 #include "mozilla/dom/WebComponentsBinding.h"
 #include "mozilla/dom/DocGroup.h"
 #include "nsHTMLTags.h"
 #include "jsapi.h"
 
 namespace mozilla {
 namespace dom {
 
+//-----------------------------------------------------
+// CustomElementUpgradeReaction
+
+class CustomElementUpgradeReaction final : public CustomElementReaction
+{
+public:
+  explicit CustomElementUpgradeReaction(CustomElementDefinition* aDefinition)
+    : mDefinition(aDefinition)
+  {
+#if DEBUG
+    mIsUpgradeReaction = true;
+#endif
+  }
+
+private:
+  virtual void Invoke(Element* aElement, ErrorResult& aRv) override
+  {
+    CustomElementRegistry::Upgrade(aElement, mDefinition, aRv);
+  }
+
+  CustomElementDefinition* mDefinition;
+};
+
+//-----------------------------------------------------
+// CustomElementCallbackReaction
+
+class CustomElementCallbackReaction final : public CustomElementReaction
+{
+  public:
+    explicit CustomElementCallbackReaction(UniquePtr<CustomElementCallback> aCustomElementCallback)
+      : mCustomElementCallback(Move(aCustomElementCallback))
+    {
+    }
+
+    virtual void Traverse(nsCycleCollectionTraversalCallback& aCb) const override
+    {
+      mCustomElementCallback->Traverse(aCb);
+    }
+
+  private:
+    virtual void Invoke(Element* aElement, ErrorResult& aRv) override
+    {
+      mCustomElementCallback->Call();
+    }
+
+    UniquePtr<CustomElementCallback> mCustomElementCallback;
+};
+
+//-----------------------------------------------------
+// CustomElementCallback
+
 void
 CustomElementCallback::Call()
 {
   IgnoredErrorResult rv;
   switch (mType) {
     case nsIDocument::eConnected:
       static_cast<LifecycleConnectedCallback *>(mCallback.get())->Call(mThisObject, rv);
       break;
@@ -82,16 +133,17 @@ CustomElementConstructor::Construct(cons
 
   RefPtr<Element> element;
   if (NS_FAILED(UNWRAP_OBJECT(Element, &result, element))) {
     return nullptr;
   }
 
   return element.forget();
 }
+
 //-----------------------------------------------------
 // CustomElementData
 
 CustomElementData::CustomElementData(nsAtom* aType)
   : CustomElementData(aType, CustomElementData::State::eUndefined)
 {
 }
 
@@ -1142,29 +1194,10 @@ CustomElementDefinition::CustomElementDe
     mConstructor(new CustomElementConstructor(aConstructor)),
     mObservedAttributes(Move(aObservedAttributes)),
     mPrototype(aPrototype),
     mCallbacks(aCallbacks),
     mDocOrder(aDocOrder)
 {
 }
 
-
-//-----------------------------------------------------
-// CustomElementUpgradeReaction
-
-/* virtual */ void
-CustomElementUpgradeReaction::Invoke(Element* aElement, ErrorResult& aRv)
-{
-  CustomElementRegistry::Upgrade(aElement, mDefinition, aRv);
-}
-
-//-----------------------------------------------------
-// CustomElementCallbackReaction
-
-/* virtual */ void
-CustomElementCallbackReaction::Invoke(Element* aElement, ErrorResult& aRv)
-{
-  mCustomElementCallback->Call();
-}
-
 } // namespace dom
 } // namespace mozilla

--- a/dom/base/CustomElementRegistry.h
+++ b/dom/base/CustomElementRegistry.h
@@ -212,51 +212,16 @@ public:
     return mIsUpgradeReaction;
   }
 
 protected:
   bool mIsUpgradeReaction = false;
 #endif
 };
 
-class CustomElementUpgradeReaction final : public CustomElementReaction
-{
-public:
-  explicit CustomElementUpgradeReaction(CustomElementDefinition* aDefinition)
-    : mDefinition(aDefinition)
-  {
-#if DEBUG
-    mIsUpgradeReaction = true;
-#endif
-  }
-
-private:
-   virtual void Invoke(Element* aElement, ErrorResult& aRv) override;
-
-   CustomElementDefinition* mDefinition;
-};
-
-class CustomElementCallbackReaction final : public CustomElementReaction
-{
-  public:
-    explicit CustomElementCallbackReaction(UniquePtr<CustomElementCallback> aCustomElementCallback)
-      : mCustomElementCallback(Move(aCustomElementCallback))
-    {
-    }
-
-    virtual void Traverse(nsCycleCollectionTraversalCallback& aCb) const override
-    {
-      mCustomElementCallback->Traverse(aCb);
-    }
-
-  private:
-    virtual void Invoke(Element* aElement, ErrorResult& aRv) override;
-    UniquePtr<CustomElementCallback> mCustomElementCallback;
-};
-
 // https://html.spec.whatwg.org/multipage/scripting.html#custom-element-reactions-stack
 class CustomElementReactionsStack
 {
 public:
   NS_INLINE_DECL_REFCOUNTING(CustomElementReactionsStack)
 
   CustomElementReactionsStack()
     : mIsBackupQueueProcessing(false)