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diff --git a/xpcom/ds/nsStringEnumerator.h b/xpcom/ds/nsStringEnumerator.h
new file mode 100644
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+++ b/xpcom/ds/nsStringEnumerator.h
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+/* -*- 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/. */
+
+#ifndef nsStringEnumerator_h
+#define nsStringEnumerator_h
+
+#include "nsIStringEnumerator.h"
+#include "nsStringFwd.h"
+#include "nsTArrayForwardDeclare.h"
+
+class nsStringEnumeratorBase : public nsIStringEnumerator,
+                               public nsIUTF8StringEnumerator {
+ public:
+  NS_DECL_NSISTRINGENUMERATORBASE
+
+  NS_IMETHOD GetNext(nsAString&) override;
+
+  using nsIUTF8StringEnumerator::GetNext;
+
+ protected:
+  virtual ~nsStringEnumeratorBase() = default;
+};
+
+// nsIStringEnumerator/nsIUTF8StringEnumerator implementations
+//
+// Currently all implementations support both interfaces. The
+// constructors below provide the most common interface for the given
+// type (i.e. nsIStringEnumerator for char16_t* strings, and so
+// forth) but any resulting enumerators can be queried to the other
+// type. Internally, the enumerators will hold onto the type that was
+// passed in and do conversion if GetNext() for the other type of
+// string is called.
+
+// There are a few different types of enumerators:
+
+//
+// These enumerators hold a pointer to the array. Be careful
+// because modifying the array may confuse the iterator, especially if
+// you insert or remove elements in the middle of the array.
+//
+
+// The non-adopting enumerator requires that the array sticks around
+// at least as long as the enumerator does. These are for constant
+// string arrays that the enumerator does not own, this could be used
+// in VERY specialized cases such as when the provider KNOWS that the
+// string enumerator will be consumed immediately, or will at least
+// outlast the array.
+// For example:
+//
+// nsTArray<nsCString> array;
+// array.AppendCString("abc");
+// array.AppendCString("def");
+// NS_NewStringEnumerator(&enumerator, &array, true);
+//
+// // call some internal method which iterates the enumerator
+// InternalMethod(enumerator);
+// NS_RELEASE(enumerator);
+//
+[[nodiscard]] nsresult NS_NewStringEnumerator(nsIStringEnumerator** aResult,
+                                              const nsTArray<nsString>* aArray,
+                                              nsISupports* aOwner);
+[[nodiscard]] nsresult NS_NewUTF8StringEnumerator(
+    nsIUTF8StringEnumerator** aResult, const nsTArray<nsCString>* aArray);
+
+[[nodiscard]] nsresult NS_NewStringEnumerator(nsIStringEnumerator** aResult,
+                                              const nsTArray<nsString>* aArray);
+
+// Adopting string enumerators assume ownership of the array and will
+// call |operator delete| on the array when the enumerator is destroyed
+// this is useful when the provider creates an array solely for the
+// purpose of creating the enumerator.
+// For example:
+//
+// nsTArray<nsCString>* array = new nsTArray<nsCString>;
+// array->AppendString("abcd");
+// NS_NewAdoptingStringEnumerator(&result, array);
+[[nodiscard]] nsresult NS_NewAdoptingStringEnumerator(
+    nsIStringEnumerator** aResult, nsTArray<nsString>* aArray);
+
+[[nodiscard]] nsresult NS_NewAdoptingUTF8StringEnumerator(
+    nsIUTF8StringEnumerator** aResult, nsTArray<nsCString>* aArray);
+
+// these versions take a refcounted "owner" which will be addreffed
+// when the enumerator is created, and destroyed when the enumerator
+// is released. This allows providers to give non-owning pointers to
+// ns*StringArray member variables without worrying about lifetime
+// issues
+// For example:
+//
+// nsresult MyClass::Enumerate(nsIUTF8StringEnumerator** aResult) {
+//     mCategoryList->AppendString("abcd");
+//     return NS_NewStringEnumerator(aResult, mCategoryList, this);
+// }
+//
+[[nodiscard]] nsresult NS_NewUTF8StringEnumerator(
+    nsIUTF8StringEnumerator** aResult, const nsTArray<nsCString>* aArray,
+    nsISupports* aOwner);
+
+#endif  // defined nsStringEnumerator_h