--- a/xpcom/glue/nsTArray.h
+++ b/xpcom/glue/nsTArray.h
@@ -815,17 +815,19 @@ public:
   operator const FallibleTArray<E>&() const {
     return *reinterpret_cast<const FallibleTArray<E>*>(this);
   }
 
   // The array's assignment operator performs a 'deep' copy of the given
   // array.  It is optimized to reuse existing storage if possible.
   // @param other  The array object to copy.
   self_type& operator=(const self_type& other) {
-    ReplaceElementsAt(0, Length(), other.Elements(), other.Length());
+    if (this != &other) {
+      ReplaceElementsAt(0, Length(), other.Elements(), other.Length());
+    }
     return *this;
   }
 
   // Return true if this array has the same length and the same
   // elements as |other|.
   template<typename Allocator>
   bool operator==(const nsTArray_Impl<E, Allocator>& other) const {
     size_type len = Length();