diff --git a/xpcom/glue/nsTArray.h b/xpcom/glue/nsTArray.h
index 5d58ae5849a..1e9d0e0e5eb 100644
--- a/xpcom/glue/nsTArray.h
+++ b/xpcom/glue/nsTArray.h
@@ -1175,31 +1175,6 @@ public:
   //
   // Mutation methods
   //
-
-  template<class Allocator, typename ActualAlloc = Alloc>
-  typename ActualAlloc::ResultType Assign(
-      const nsTArray_Impl<E, Allocator>& aOther)
-  {
-    return ActualAlloc::ConvertBoolToResultType(
-      !!ReplaceElementsAt<E, ActualAlloc>(0, Length(),
-                                          aOther.Elements(), aOther.Length()));
-  }
-
-  template<class Allocator>
-  /* MOZ_WARN_UNUSED_RESULT */
-  bool Assign(const nsTArray_Impl<E, Allocator>& aOther,
-              const mozilla::fallible_t&)
-  {
-    return Assign<Allocator, FallibleAlloc>(aOther);
-  }
-
-  template<class Allocator>
-  void Assign(nsTArray_Impl<E, Allocator>&& aOther)
-  {
-    Clear();
-    SwapElements(aOther);
-  }
-
   // This method call the destructor on each element of the array, empties it,
   // but does not shrink the array's capacity.
   // See also SetLengthAndRetainStorage.
diff --git a/xpcom/tests/gtest/TestTArray.cpp b/xpcom/tests/gtest/TestTArray.cpp
deleted file mode 100644
index 7bcb63a28f9..00000000000
--- a/xpcom/tests/gtest/TestTArray.cpp
+++ /dev/null
@@ -1,55 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include "nsTArray.h"
-#include "gtest/gtest.h"
-
-using namespace mozilla;
-
-namespace TestTArray {
-
-const nsTArray<int>& DummyArray()
-{
-  static nsTArray<int> sArray;
-  if (sArray.IsEmpty()) {
-    const int data[] = {4, 1, 2, 8};
-    sArray.AppendElements(data, ArrayLength(data));
-  }
-  return sArray;
-}
-
-// This returns an invalid nsTArray with a huge length in order to test that
-// fallible operations actually fail.
-const nsTArray<int>& FakeHugeArray()
-{
-  static nsTArray<int> sArray;
-#ifdef DEBUG
-  if (sArray.IsEmpty()) {
-    sArray.AppendElement();
-    ((nsTArrayHeader*)sArray.DebugGetHeader())->mLength = UINT32_MAX;
-  }
-#endif
-  return sArray;
-}
-
-TEST(TArray, assign)
-{
-  nsTArray<int> array;
-  array.Assign(DummyArray());
-  ASSERT_EQ(DummyArray(), array);
-
-  ASSERT_TRUE(array.Assign(DummyArray(), fallible));
-  ASSERT_EQ(DummyArray(), array);
-
-  ASSERT_FALSE(array.Assign(FakeHugeArray(), fallible));
-
-  nsTArray<int> array2;
-  array2.Assign(Move(array));
-  ASSERT_TRUE(array.IsEmpty());
-  ASSERT_EQ(DummyArray(), array2);
-}
-
-}
diff --git a/xpcom/tests/gtest/moz.build b/xpcom/tests/gtest/moz.build
index 6c47bcee91c..32bd5d11747 100644
--- a/xpcom/tests/gtest/moz.build
+++ b/xpcom/tests/gtest/moz.build
@@ -17,7 +17,6 @@ UNIFIED_SOURCES += [
     'TestStrings.cpp',
     'TestStringStream.cpp',
     'TestSynchronization.cpp',
-    'TestTArray.cpp',
     'TestThreadPool.cpp',
     'TestThreads.cpp',
     'TestTimeStamp.cpp',