--- a/js/xpconnect/src/XPCJSRuntime.cpp
+++ b/js/xpconnect/src/XPCJSRuntime.cpp
@@ -653,21 +653,23 @@ XPCJSRuntime::TraverseAdditionalNativeRo
     for (XPCRootSetElem* e = mVariantRoots; e ; e = e->GetNextRoot()) {
         XPCTraceableVariant* v = static_cast<XPCTraceableVariant*>(e);
         if (nsCCUncollectableMarker::InGeneration(cb,
                                                   v->CCGeneration())) {
            JS::Value val = v->GetJSValPreserveColor();
            if (val.isObject() && !JS::ObjectIsMarkedGray(&val.toObject()))
                continue;
         }
-        cb.NoteXPCOMRoot(v);
+        cb.NoteXPCOMRoot(v,
+                         XPCTraceableVariant::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant());
     }
 
     for (XPCRootSetElem* e = mWrappedJSRoots; e ; e = e->GetNextRoot()) {
-        cb.NoteXPCOMRoot(ToSupports(static_cast<nsXPCWrappedJS*>(e)));
+        cb.NoteXPCOMRoot(ToSupports(static_cast<nsXPCWrappedJS*>(e)),
+                         nsXPCWrappedJS::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant());
     }
 }
 
 void
 XPCJSRuntime::UnmarkSkippableJSHolders()
 {
     CycleCollectedJSRuntime::UnmarkSkippableJSHolders();
 }

--- a/xpcom/base/nsCycleCollectionNoteRootCallback.h
+++ b/xpcom/base/nsCycleCollectionNoteRootCallback.h
@@ -8,17 +8,20 @@
 #define nsCycleCollectionNoteRootCallback_h__
 
 class nsCycleCollectionParticipant;
 class nsISupports;
 
 class nsCycleCollectionNoteRootCallback
 {
 public:
-  NS_IMETHOD_(void) NoteXPCOMRoot(nsISupports* aRoot) = 0;
+  // aRoot must be canonical (ie the result of QIing to nsCycleCollectionISupports).
+  NS_IMETHOD_(void) NoteXPCOMRoot(nsISupports* aRoot,
+                                  nsCycleCollectionParticipant* aParticipant) = 0;
+
   NS_IMETHOD_(void) NoteJSRoot(JSObject* aRoot) = 0;
   NS_IMETHOD_(void) NoteNativeRoot(void* aRoot,
                                    nsCycleCollectionParticipant* aParticipant) = 0;
 
   NS_IMETHOD_(void) NoteWeakMapping(JSObject* aMap, JS::GCCellPtr aKey,
                                     JSObject* aKeyDelegate, JS::GCCellPtr aVal) = 0;
 
   bool WantAllTraces() const { return mWantAllTraces; }

--- a/xpcom/base/nsCycleCollector.cpp
+++ b/xpcom/base/nsCycleCollector.cpp
@@ -2097,17 +2097,18 @@ private:
 
   void SetLastChild()
   {
     mCurrPi->SetLastChild(mEdgeBuilder.Mark());
   }
 
 public:
   // nsCycleCollectionNoteRootCallback methods.
-  NS_IMETHOD_(void) NoteXPCOMRoot(nsISupports* aRoot);
+  NS_IMETHOD_(void) NoteXPCOMRoot(nsISupports* aRoot,
+                                  nsCycleCollectionParticipant* aParticipant);
   NS_IMETHOD_(void) NoteJSRoot(JSObject* aRoot);
   NS_IMETHOD_(void) NoteNativeRoot(void* aRoot,
                                    nsCycleCollectionParticipant* aParticipant);
   NS_IMETHOD_(void) NoteWeakMapping(JSObject* aMap, JS::GCCellPtr aKey,
                                     JSObject* aKdelegate, JS::GCCellPtr aVal);
 
   // nsCycleCollectionTraversalCallback methods.
   NS_IMETHOD_(void) DescribeRefCountedNode(nsrefcnt aRefCount,
@@ -2290,26 +2291,28 @@ CCGraphBuilder::BuildGraph(SliceBudget& 
   }
 
   mCurrNode = nullptr;
 
   return true;
 }
 
 NS_IMETHODIMP_(void)
-CCGraphBuilder::NoteXPCOMRoot(nsISupports* aRoot)
+CCGraphBuilder::NoteXPCOMRoot(nsISupports* aRoot,
+                              nsCycleCollectionParticipant* aParticipant)
 {
-  aRoot = CanonicalizeXPCOMParticipant(aRoot);
-  NS_ASSERTION(aRoot,
-               "Don't add objects that don't participate in collection!");
-
+  MOZ_ASSERT(aRoot == CanonicalizeXPCOMParticipant(aRoot));
+
+#ifdef DEBUG
   nsXPCOMCycleCollectionParticipant* cp;
   ToParticipant(aRoot, &cp);
-
-  NoteRoot(aRoot, cp);
+  MOZ_ASSERT(aParticipant == cp);
+#endif
+
+  NoteRoot(aRoot, aParticipant);
 }
 
 NS_IMETHODIMP_(void)
 CCGraphBuilder::NoteJSRoot(JSObject* aRoot)
 {
   if (JS::Zone* zone = MergeZone(JS::GCCellPtr(aRoot))) {
     NoteRoot(zone, mJSZoneParticipant);
   } else {