--- a/xpcom/glue/nsTArray.h
+++ b/xpcom/glue/nsTArray.h
@@ -2012,16 +2012,26 @@ public:
     NS_QuickSort(Elements(), Length(), sizeof(elem_type),
                  Compare<Comparator>, const_cast<Comparator*>(&aComp));
   }
 
   // A variation on the Sort method defined above that assumes that
   // 'operator<' is defined for elem_type.
   void Sort() { Sort(nsDefaultComparator<elem_type, elem_type>()); }
 
+  // This method reverses the array in place.
+  void Reverse()
+  {
+    elem_type* elements = Elements();
+    const size_type len = Length();
+    for (index_type i = 0, iend = len / 2; i < iend; ++i) {
+      mozilla::Swap(elements[i], elements[len - i - 1]);
+    }
+  }
+
 protected:
   using base_type::Hdr;
   using base_type::ShrinkCapacity;
 
   // This method invokes elem_type's destructor on a range of elements.
   // @param aStart The index of the first element to destroy.
   // @param aCount The number of elements to destroy.
   void DestructRange(index_type aStart, size_type aCount)