diff --git a/js/src/gc/Heap.h b/js/src/gc/Heap.h
index 2ecb7e9122a8..43a4dfd619fa 100644
--- a/js/src/gc/Heap.h
+++ b/js/src/gc/Heap.h
@@ -261,6 +261,8 @@ struct Cell
     // May be overridden by GC thing kinds that have a compartment pointer.
     inline JSCompartment* maybeCompartment() const { return nullptr; }
 
+    // The StoreBuffer used to record incoming pointers from the tenured heap.
+    // This will return nullptr for a tenured cell.
     inline StoreBuffer* storeBuffer() const;
 
     inline JS::TraceKind getTraceKind() const;
@@ -769,25 +771,26 @@ FreeSpan::checkRange(uintptr_t first, uintptr_t last, const Arena* arena) const
  */
 struct ChunkTrailer
 {
-    /* Construct a Nursery ChunkTrailer. */
+    // Construct a Nursery ChunkTrailer.
     ChunkTrailer(JSRuntime* rt, StoreBuffer* sb)
       : location(ChunkLocation::Nursery), storeBuffer(sb), runtime(rt)
     {}
 
-    /* Construct a Tenured heap ChunkTrailer. */
+    // Construct a Tenured heap ChunkTrailer.
     explicit ChunkTrailer(JSRuntime* rt)
       : location(ChunkLocation::TenuredHeap), storeBuffer(nullptr), runtime(rt)
     {}
 
   public:
-    /* The index the chunk in the nursery, or LocationTenuredHeap. */
+    // The index of the chunk in the nursery, or LocationTenuredHeap.
     ChunkLocation   location;
     uint32_t        padding;
 
-    /* The store buffer for writes to things in this chunk or nullptr. */
+    // The store buffer for pointers from tenured things to things in this
+    // chunk. Will be non-null only for nursery chunks.
     StoreBuffer*    storeBuffer;
 
-    /* This provides quick access to the runtime from absolutely anywhere. */
+    // Provide quick access to the runtime from absolutely anywhere.
     JSRuntime*      runtime;
 };
 
diff --git a/js/src/gc/Statistics.h b/js/src/gc/Statistics.h
index 7f7423d158f9..6325ffd55c75 100644
--- a/js/src/gc/Statistics.h
+++ b/js/src/gc/Statistics.h
@@ -333,13 +333,13 @@ struct Statistics
     SliceRange sliceRange() const { return slices.all(); }
     size_t slicesLength() const { return slices.length(); }
 
-    /* Occasionally print header lines for profiling information. */
+    // Occasionally print header lines for profiling information.
     void maybePrintProfileHeaders();
 
-    /* Print header line for profile times. */
+    // Print header line for profile times.
     void printProfileHeader();
 
-    /* Print total profile times on shutdown. */
+    // Print total profile times on shutdown.
     void printTotalProfileTimes();
 
   private:
diff --git a/js/src/jsobj.h b/js/src/jsobj.h
index 4855b5655cc2..edee272f81bf 100644
--- a/js/src/jsobj.h
+++ b/js/src/jsobj.h
@@ -670,7 +670,8 @@ JSObject::writeBarrierPost(void* cellp, JSObject* prev, JSObject* next)
         return;
     }
 
-    // Remove the prev entry if the new value does not need it.
+    // Remove the prev entry if the new value does not need it. There will only
+    // be a prev entry if the prev value was in the nursery.
     if (prev && (buffer = prev->storeBuffer()))
         buffer->unputCell(static_cast<js::gc::Cell**>(cellp));
 }