diff --git a/xpcom/glue/nsCOMArray.cpp b/xpcom/glue/nsCOMArray.cpp
index 4054426e62a7..dc2d536608bd 100644
--- a/xpcom/glue/nsCOMArray.cpp
+++ b/xpcom/glue/nsCOMArray.cpp
@@ -61,6 +61,26 @@ nsCOMArray_base::~nsCOMArray_base()
     }                        
 }
 
+PRInt32
+nsCOMArray_base::IndexOfObject(nsISupports* aObject) const {
+    NS_ENSURE_TRUE(aObject, -1);
+    nsCOMPtr<nsISupports> supports = do_QueryInterface(aObject);
+    NS_ENSURE_TRUE(supports, -1);
+
+    PRInt32 i, count;
+    PRInt32 retval = -1;
+    count = mArray.Count();
+    for (i = 0; i < count; ++i) {
+        nsCOMPtr<nsISupports> arrayItem =
+            do_QueryInterface(NS_REINTERPRET_CAST(nsISupports*,mArray.ElementAt(i)));
+        if (arrayItem == supports) {
+            retval = i;
+            break;
+        }
+    }
+    return retval;
+}
+
 PRBool
 nsCOMArray_base::InsertObjectAt(nsISupports* aObject, PRInt32 aIndex) {
     PRBool result = mArray.InsertElementAt(aObject, aIndex);
diff --git a/xpcom/glue/nsCOMArray.h b/xpcom/glue/nsCOMArray.h
index c69eb72b471c..996a7504878f 100644
--- a/xpcom/glue/nsCOMArray.h
+++ b/xpcom/glue/nsCOMArray.h
@@ -60,6 +60,8 @@ protected:
         return mArray.IndexOf(aObject);
     }
 
+    PRInt32 IndexOfObject(nsISupports* aObject) const;
+
     PRBool EnumerateForwards(nsVoidArrayEnumFunc aFunc, void* aData) {
         return mArray.EnumerateForwards(aFunc, aData);
     }
@@ -150,10 +152,21 @@ class nsCOMArray : public nsCOMArray_base
     }
 
     // index of the element in question.. does NOT refcount
+    // note: this does not check COM object identity. Use
+    // IndexOfObject() for that purpose
     PRInt32 IndexOf(T* aObject) const {
         return nsCOMArray_base::IndexOf(NS_STATIC_CAST(nsISupports*, aObject));
     }
 
+    // index of the element in question.. be careful!
+    // this is much slower than IndexOf() because it uses
+    // QueryInterface to determine actual COM identity of the object
+    // if you need to do this frequently then consider enforcing
+    // COM object identity before adding/comparing elements
+    PRInt32 IndexOfObject(T* aObject) const {
+        return nsCOMArray_base::IndexOfObject(NS_STATIC_CAST(nsISupports*, aObject));
+    }
+
     // inserts aObject at aIndex, shifting the objects at aIndex and
     // later to make space
     PRBool InsertObjectAt(T* aObject, PRInt32 aIndex) {