--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -3484,18 +3484,18 @@ MediaStreamGraphImpl::CollectReports(nsI
     rv = aHandleReport->Callback(EmptyCString(), _path,                     \
                                  KIND_HEAP, UNITS_BYTES, _amount,           \
                                  NS_LITERAL_CSTRING(_desc), aData);         \
     NS_ENSURE_SUCCESS(rv, rv);                                              \
   } while (0)
 
   for (size_t i = 0; i < mAudioStreamSizes.Length(); i++) {
     const AudioNodeSizes& usage = mAudioStreamSizes[i];
-    const char* const nodeType =  usage.mNodeType.IsEmpty() ?
-                                  "<unknown>" : usage.mNodeType.get();
+    const char* const nodeType =
+      usage.mNodeType ? usage.mNodeType : "<unknown>";
 
     nsPrintfCString domNodePath("explicit/webaudio/audio-node/%s/dom-nodes",
                                 nodeType);
     REPORT(domNodePath, usage.mDomNode,
            "Memory used by AudioNode DOM objects (Web Audio).");
 
     nsPrintfCString enginePath("explicit/webaudio/audio-node/%s/engine-objects",
                                nodeType);

--- a/dom/media/MediaStreamGraph.h
+++ b/dom/media/MediaStreamGraph.h
@@ -431,17 +431,17 @@ public:
  * Helper struct used to keep track of memory usage by AudioNodes.
  */
 struct AudioNodeSizes
 {
   AudioNodeSizes() : mDomNode(0), mStream(0), mEngine(0), mNodeType() {}
   size_t mDomNode;
   size_t mStream;
   size_t mEngine;
-  nsCString mNodeType;
+  const char* mNodeType;
 };
 
 class MediaStreamGraphImpl;
 class SourceMediaStream;
 class ProcessedMediaStream;
 class MediaInputPort;
 class AudioNodeEngine;
 class AudioNodeExternalInputStream;

--- a/dom/media/webaudio/AudioNode.h
+++ b/dom/media/webaudio/AudioNode.h
@@ -202,16 +202,18 @@ public:
   // Do not call MarkInactive from a node destructor.  If the destructor is
   // called, then the node is already inactive.
   // MarkInactive() may delete |this|.
   void MarkInactive() { Context()->UnregisterActiveNode(this); }
 
   virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
   virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
 
+  // Returns a string from constant static storage identifying the dom node
+  // type.
   virtual const char* NodeType() const = 0;
 
 private:
   virtual void LastRelease() override
   {
     // We are about to be deleted, disconnect the object from the graph before
     // the derived type is destroyed.
     DisconnectFromGraph();