diff --git a/xpcom/glue/nsCOMArray.h b/xpcom/glue/nsCOMArray.h
index 35941c3a3097..50300a95b67b 100644
--- a/xpcom/glue/nsCOMArray.h
+++ b/xpcom/glue/nsCOMArray.h
@@ -121,6 +121,16 @@ public:
                            : true;
     }
 
+    // Measures the size of the array's element storage, and if
+    // |aSizeOfElement| is non-NULL, measures the size of things pointed to by
+    // elements.
+    size_t SizeOfExcludingThis(
+             nsVoidArraySizeOfElementIncludingThisFunc aSizeOfElementIncludingThis,
+             nsMallocSizeOfFun aMallocSizeOf, void* aData = NULL) const {
+        return mArray.SizeOfExcludingThis(aSizeOfElementIncludingThis,
+                                          aMallocSizeOf, aData);
+    }
+    
 private:
     
     // the actual storage
@@ -276,6 +286,20 @@ class nsCOMArray : public nsCOMArray_base
         return nsCOMArray_base::RemoveObjectsAt(aIndex, aCount);
     }
 
+    // Each element in an nsCOMArray<T> is actually a T*, so this function is
+    // "IncludingThis" rather than "ExcludingThis" because it needs to measure
+    // the memory taken by the T itself as well as anything it points to.
+    typedef size_t (* nsCOMArraySizeOfElementIncludingThisFunc)
+        (T* aElement, nsMallocSizeOfFun aMallocSizeOf, void *aData);
+    
+    size_t SizeOfExcludingThis(
+             nsCOMArraySizeOfElementIncludingThisFunc aSizeOfElementIncludingThis, 
+             nsMallocSizeOfFun aMallocSizeOf, void *aData = NULL) const {
+        return nsCOMArray_base::SizeOfExcludingThis(
+                 nsVoidArraySizeOfElementIncludingThisFunc(aSizeOfElementIncludingThis),
+                 aMallocSizeOf, aData);
+    }
+
 private:
 
     // don't implement these!
diff --git a/xpcom/glue/nsVoidArray.cpp b/xpcom/glue/nsVoidArray.cpp
index f8904edfb286..0ae56d1d2ec5 100644
--- a/xpcom/glue/nsVoidArray.cpp
+++ b/xpcom/glue/nsVoidArray.cpp
@@ -717,10 +717,22 @@ bool nsVoidArray::EnumerateForwards(nsVoidArrayEnumFunc aFunc, void* aData)
   PRInt32 index = -1;
   bool    running = true;
 
-  if (mImpl)
-  {
-    while (running && (++index < mImpl->mCount))
-    {
+  if (mImpl) {
+    while (running && (++index < mImpl->mCount)) {
+      running = (*aFunc)(mImpl->mArray[index], aData);
+    }
+  }
+  return running;
+}
+
+bool nsVoidArray::EnumerateForwards(nsVoidArrayEnumFuncConst aFunc,
+                                    void* aData) const
+{
+  PRInt32 index = -1;
+  bool    running = true;
+
+  if (mImpl) {
+    while (running && (++index < mImpl->mCount)) {
       running = (*aFunc)(mImpl->mArray[index], aData);
     }
   }
@@ -742,6 +754,42 @@ bool nsVoidArray::EnumerateBackwards(nsVoidArrayEnumFunc aFunc, void* aData)
   return running;
 }
 
+struct SizeOfElementIncludingThisData
+{
+  size_t mSize;
+  nsVoidArraySizeOfElementIncludingThisFunc mSizeOfElementIncludingThis;
+  nsMallocSizeOfFun mMallocSizeOf;
+  void *mData;      // the arg passed by the user
+};
+
+static bool
+SizeOfElementIncludingThisEnumerator(const void *aElement, void *aData)
+{
+  SizeOfElementIncludingThisData *d = (SizeOfElementIncludingThisData *)aData;
+  d->mSize += d->mSizeOfElementIncludingThis(aElement, d->mMallocSizeOf, d->mData);
+  return true;
+}
+
+size_t
+nsVoidArray::SizeOfExcludingThis(
+  nsVoidArraySizeOfElementIncludingThisFunc aSizeOfElementIncludingThis,
+  nsMallocSizeOfFun aMallocSizeOf, void* aData) const
+{
+  size_t n = 0;
+  // Measure the element storage.
+  if (mImpl) {
+    n += aMallocSizeOf(mImpl);
+  }
+  // Measure things pointed to by the elements.
+  if (aSizeOfElementIncludingThis) { 
+    SizeOfElementIncludingThisData data2 =
+      { 0, aSizeOfElementIncludingThis, aMallocSizeOf, aData };
+    EnumerateForwards(SizeOfElementIncludingThisEnumerator, &data2);
+    n += data2.mSize;
+  }
+  return n;
+}
+
 //----------------------------------------------------------------
 // nsAutoVoidArray
 
diff --git a/xpcom/glue/nsVoidArray.h b/xpcom/glue/nsVoidArray.h
index 36cc9ba0f518..9d3415b00843 100644
--- a/xpcom/glue/nsVoidArray.h
+++ b/xpcom/glue/nsVoidArray.h
@@ -47,6 +47,12 @@ typedef int (* nsVoidArrayComparatorFunc)
 
 // Enumerator callback function. Return false to stop
 typedef bool (* nsVoidArrayEnumFunc)(void* aElement, void *aData);
+typedef bool (* nsVoidArrayEnumFuncConst)(const void* aElement, void *aData);
+
+// SizeOfExcludingThis callback function.
+typedef size_t (* nsVoidArraySizeOfElementIncludingThisFunc)(const void* aElement,
+                                                             nsMallocSizeOfFun aMallocSizeOf,
+                                                             void *aData);
 
 /// A basic zero-based array of void*'s that manages its own memory
 class NS_COM_GLUE nsVoidArray {
@@ -127,8 +133,16 @@ public:
   void Sort(nsVoidArrayComparatorFunc aFunc, void* aData);
 
   bool EnumerateForwards(nsVoidArrayEnumFunc aFunc, void* aData);
+  bool EnumerateForwards(nsVoidArrayEnumFuncConst aFunc, void* aData) const;
   bool EnumerateBackwards(nsVoidArrayEnumFunc aFunc, void* aData);
 
+  // Measures the size of the array's element storage, and if
+  // |aSizeOfElementIncludingThis| is non-NULL, measures the size of things
+  // pointed to by elements.
+  size_t SizeOfExcludingThis(
+           nsVoidArraySizeOfElementIncludingThisFunc aSizeOfElementIncludingThis,
+           nsMallocSizeOfFun aMallocSizeOf, void* aData = NULL) const;
+
 protected:
   bool GrowArrayBy(PRInt32 aGrowBy);