Adding upstream version 115.8.0esr.upstream/115.8.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

22 files changed, 2327 insertions, 0 deletions

diff --git a/extensions/spellcheck/hunspell/glue/PRemoteSpellcheckEngine.ipdl b/extensions/spellcheck/hunspell/glue/PRemoteSpellcheckEngine.ipdl
new file mode 100644
index 0000000000..c327d97e65
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/PRemoteSpellcheckEngine.ipdl
@@ -0,0 +1,46 @@
+/* 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 protocol PContent;
+
+include "mozilla/RemoteSpellCheckEngineParent.h";
+include "mozilla/RemoteSpellCheckEngineChild.h";
+
+namespace mozilla {
+
+[ManualDealloc, ChildImpl="RemoteSpellcheckEngineChild", ParentImpl="RemoteSpellcheckEngineParent"]
+sync protocol PRemoteSpellcheckEngine {
+  manager PContent;
+
+parent:
+  async __delete__();
+
+  async CheckAsync(nsString[] aWord) returns (bool[] aIsMisspelled);
+
+  sync SetDictionary(nsCString aDictionary) returns (bool success);
+
+  /*
+   * Set multiple current dictionaries from a list of dictionary names.
+   *
+   * @aDictionaries An array of dictionary names to use. If the array is empty,
+   *                no dictionary will be used.
+   * @aSuccess      true if setting the dictionaries succeeded, false otherwise.
+   */
+  async SetDictionaries(nsCString[] aDictionaries) returns (bool success);
+
+  async Suggest(nsString aWord, uint32_t aCount) returns (nsString[] aSuggestions);
+
+  /*
+   * Set current dictionary from list of dictionary name.
+   *
+   * @aList         A list of dictionary name.  If a string into this list is
+   *                empty string, dictionary selection is reset
+   * @aSuccess      true if setting dictionary is successful
+   * @aDictionary   Return current dictionary name that set by this method.
+   */
+  async SetDictionaryFromList(nsCString[] aList)
+           returns (bool aSuccess, nsCString aDictionary);
+};
+
+} // namespace mozilla
diff --git a/extensions/spellcheck/hunspell/glue/RLBoxHunspell.cpp b/extensions/spellcheck/hunspell/glue/RLBoxHunspell.cpp
new file mode 100644
index 0000000000..b3a1990ceb
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/RLBoxHunspell.cpp
@@ -0,0 +1,256 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "mozilla/Assertions.h"
+#ifdef MOZ_WASM_SANDBOXING_HUNSPELL
+#  include "mozilla/ipc/LibrarySandboxPreload.h"
+#endif
+#include "RLBoxHunspell.h"
+#include "mozHunspellRLBoxGlue.h"
+#include "mozHunspellRLBoxHost.h"
+#include "nsThread.h"
+
+using namespace rlbox;
+using namespace mozilla;
+
+// Helper function for allocating and copying std::string into sandbox
+static tainted_hunspell<char*> allocStrInSandbox(
+    rlbox_sandbox_hunspell& aSandbox, const std::string& str) {
+  size_t size = str.size() + 1;
+  tainted_hunspell<char*> t_str = aSandbox.malloc_in_sandbox<char>(size);
+  if (t_str) {
+    rlbox::memcpy(aSandbox, t_str, str.c_str(), size);
+  }
+  return t_str;
+}
+
+/* static */
+RLBoxHunspell* RLBoxHunspell::Create(const nsCString& affpath,
+                                     const nsCString& dpath) {
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
+
+  mozilla::UniquePtr<rlbox_sandbox_hunspell> sandbox(
+      new rlbox_sandbox_hunspell());
+
+#if defined(MOZ_WASM_SANDBOXING_HUNSPELL) && !defined(HAVE_64BIT_BUILD)
+  // By default, the rlbox sandbox size is smaller on 32-bit builds than the max
+  // 4GB. We may need to ask for a larger sandbox size for hunspell to
+  // spellcheck in some locales See Bug 1739669 for more details
+
+  // We first get the size of the dictionary. This is actually the first read we
+  // try on dpath and it might fail for whatever filesystem reasons (invalid
+  // path, unaccessible, ...).
+  Result<int64_t, nsresult> dictSizeResult =
+      mozHunspellFileMgrHost::GetSize(dpath);
+  NS_ENSURE_TRUE(dictSizeResult.isOk(), nullptr);
+
+  int64_t dictSize = dictSizeResult.unwrap();
+  NS_ENSURE_TRUE(dictSize >= 0, nullptr);
+
+  // Next, we compute the expected memory needed for hunspell spell checking.
+  // This will vary based on the size of the dictionary file, which varies by
+  // locale — so we size the sandbox by multiplying the file size by 4.8. This
+  // allows the 1.5MB en_US dictionary to fit in an 8MB sandbox. See bug 1739669
+  // and bug 1739761 for the analysis behind this.
+  const uint64_t expectedMaxMemory = static_cast<uint64_t>(4.8 * dictSize);
+
+  // Get a capacity of at least the expected size
+  const w2c_mem_capacity capacity = get_valid_wasm2c_memory_capacity(
+      expectedMaxMemory, true /* wasm's 32-bit memory */);
+
+  bool success =
+      sandbox->create_sandbox(/* shouldAbortOnFailure = */ false, &capacity);
+#elif defined(MOZ_WASM_SANDBOXING_HUNSPELL)
+  bool success = sandbox->create_sandbox(/* shouldAbortOnFailure = */ false);
+#else
+  sandbox->create_sandbox();
+  const bool success = true;
+#endif
+
+  NS_ENSURE_TRUE(success, nullptr);
+
+  mozilla::UniquePtr<rlbox_sandbox_hunspell, RLBoxDeleter> sandbox_initialized(
+      sandbox.release());
+
+  // Add the aff and dict files to allow list
+  if (!affpath.IsEmpty()) {
+    mozHunspellCallbacks::AllowFile(affpath);
+  }
+  if (!dpath.IsEmpty()) {
+    mozHunspellCallbacks::AllowFile(dpath);
+  }
+
+  // TODO Bug 1788857: Verify error handling in case of inaccessible file
+  return new RLBoxHunspell(std::move(sandbox_initialized), affpath, dpath);
+}
+
+RLBoxHunspell::RLBoxHunspell(
+    mozilla::UniquePtr<rlbox_sandbox_hunspell, RLBoxDeleter> aSandbox,
+    const nsCString& affpath, const nsCString& dpath)
+    : mSandbox(std::move(aSandbox)), mHandle(nullptr) {
+  // Register callbacks
+  mCreateFilemgr =
+      mSandbox->register_callback(mozHunspellCallbacks::CreateFilemgr);
+  mGetLine = mSandbox->register_callback(mozHunspellCallbacks::GetLine);
+  mGetLineNum = mSandbox->register_callback(mozHunspellCallbacks::GetLineNum);
+  mDestructFilemgr =
+      mSandbox->register_callback(mozHunspellCallbacks::DestructFilemgr);
+  mHunspellToUpperCase =
+      mSandbox->register_callback(mozHunspellCallbacks::ToUpperCase);
+  mHunspellToLowerCase =
+      mSandbox->register_callback(mozHunspellCallbacks::ToLowerCase);
+  mHunspellGetCurrentCS =
+      mSandbox->register_callback(mozHunspellCallbacks::GetCurrentCS);
+
+  mSandbox->invoke_sandbox_function(RegisterHunspellCallbacks, mCreateFilemgr,
+                                    mGetLine, mGetLineNum, mDestructFilemgr,
+                                    mHunspellToUpperCase, mHunspellToLowerCase,
+                                    mHunspellGetCurrentCS);
+
+  // Copy the affpath and dpath into the sandbox
+  // These allocations should definitely succeed as these are first allocations
+  // inside the sandbox.
+  tainted_hunspell<char*> t_affpath =
+      allocStrInSandbox(*mSandbox, affpath.get());
+  MOZ_RELEASE_ASSERT(t_affpath);
+
+  tainted_hunspell<char*> t_dpath = allocStrInSandbox(*mSandbox, dpath.get());
+  MOZ_RELEASE_ASSERT(t_dpath);
+
+  // Create handle
+  mHandle = mSandbox->invoke_sandbox_function(
+      Hunspell_create, rlbox::sandbox_const_cast<const char*>(t_affpath),
+      rlbox::sandbox_const_cast<const char*>(t_dpath));
+  MOZ_RELEASE_ASSERT(mHandle);
+
+  mSandbox->free_in_sandbox(t_dpath);
+  mSandbox->free_in_sandbox(t_affpath);
+
+  // Get dictionary encoding
+  tainted_hunspell<char*> t_enc =
+      mSandbox->invoke_sandbox_function(Hunspell_get_dic_encoding, mHandle);
+  t_enc.copy_and_verify_string([&](std::unique_ptr<char[]> enc) {
+    size_t len = std::strlen(enc.get());
+    mDicEncoding = std::string(enc.get(), len);
+  });
+}
+
+RLBoxHunspell::~RLBoxHunspell() {
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
+  // Call hunspell's destroy which frees mHandle
+  mSandbox->invoke_sandbox_function(Hunspell_destroy, mHandle);
+  mHandle = nullptr;
+
+  // Unregister callbacks
+  mDestructFilemgr.unregister();
+  mGetLineNum.unregister();
+  mGetLine.unregister();
+  mCreateFilemgr.unregister();
+  mHunspellToUpperCase.unregister();
+  mHunspellToLowerCase.unregister();
+  mHunspellGetCurrentCS.unregister();
+
+  // Clear any callback data and allow list
+  mozHunspellCallbacks::Clear();
+}
+
+// Invoking hunspell with words larger than a certain size will cause the
+// Hunspell sandbox to run out of memory. So we pick an arbitrary limit of
+// 200000 here to ensure this doesn't happen.
+static const size_t gWordSizeLimit = 200000;
+
+int RLBoxHunspell::spell(const std::string& stdWord) {
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
+
+  const int ok = 1;
+
+  if (stdWord.length() >= gWordSizeLimit) {
+    // Fail gracefully assuming the word is spelt correctly
+    return ok;
+  }
+
+  // Copy word into the sandbox
+  tainted_hunspell<char*> t_word = allocStrInSandbox(*mSandbox, stdWord);
+  if (!t_word) {
+    // Ran out of memory in the hunspell sandbox
+    // Fail gracefully assuming the word is spelt correctly
+    return ok;
+  }
+
+  // Check word
+  int good = mSandbox
+                 ->invoke_sandbox_function(
+                     Hunspell_spell, mHandle,
+                     rlbox::sandbox_const_cast<const char*>(t_word))
+                 .copy_and_verify([](int good) { return good; });
+  mSandbox->free_in_sandbox(t_word);
+  return good;
+}
+
+const std::string& RLBoxHunspell::get_dict_encoding() const {
+  return mDicEncoding;
+}
+
+// This function fails gracefully - if we run out of memory in the hunspell
+// sandbox, we return empty suggestion list
+std::vector<std::string> RLBoxHunspell::suggest(const std::string& stdWord) {
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
+
+  if (stdWord.length() >= gWordSizeLimit) {
+    return {};
+  }
+
+  // Copy word into the sandbox
+  tainted_hunspell<char*> t_word = allocStrInSandbox(*mSandbox, stdWord);
+  if (!t_word) {
+    return {};
+  }
+
+  // Allocate suggestion list in the sandbox
+  tainted_hunspell<char***> t_slst = mSandbox->malloc_in_sandbox<char**>();
+  if (!t_slst) {
+    // Free the earlier allocation
+    mSandbox->free_in_sandbox(t_word);
+    return {};
+  }
+
+  *t_slst = nullptr;
+
+  // Get suggestions
+  int nr = mSandbox
+               ->invoke_sandbox_function(
+                   Hunspell_suggest, mHandle, t_slst,
+                   rlbox::sandbox_const_cast<const char*>(t_word))
+               .copy_and_verify([](int nr) {
+                 MOZ_RELEASE_ASSERT(nr >= 0);
+                 return nr;
+               });
+
+  tainted_hunspell<char**> t_slst_ref = *t_slst;
+
+  std::vector<std::string> suggestions;
+  if (nr > 0 && t_slst_ref != nullptr) {
+    // Copy suggestions from sandbox
+    suggestions.reserve(nr);
+
+    for (int i = 0; i < nr; i++) {
+      tainted_hunspell<char*> t_sug = t_slst_ref[i];
+
+      if (t_sug) {
+        t_sug.copy_and_verify_string(
+            [&](std::string sug) { suggestions.push_back(std::move(sug)); });
+        // free the suggestion string allocated by the sandboxed hunspell
+        mSandbox->free_in_sandbox(t_sug);
+      }
+    }
+
+    // free the suggestion list allocated by the sandboxed hunspell
+    mSandbox->free_in_sandbox(t_slst_ref);
+  }
+
+  mSandbox->free_in_sandbox(t_word);
+  mSandbox->free_in_sandbox(t_slst);
+  return suggestions;
+}
diff --git a/extensions/spellcheck/hunspell/glue/RLBoxHunspell.h b/extensions/spellcheck/hunspell/glue/RLBoxHunspell.h
new file mode 100644
index 0000000000..2e5a11d936
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/RLBoxHunspell.h
@@ -0,0 +1,66 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 EXTENSIONS_SPELLCHECK_HUNSPELL_GLUE_RLBOXHUNSPELL_H_
+#define EXTENSIONS_SPELLCHECK_HUNSPELL_GLUE_RLBOXHUNSPELL_H_
+
+#include "RLBoxHunspellTypes.h"
+
+// Load general firefox configuration of RLBox
+#include "mozilla/rlbox/rlbox_config.h"
+
+#ifdef MOZ_WASM_SANDBOXING_HUNSPELL
+// Include the generated header file so that we are able to resolve the symbols
+// in the wasm binary
+#  include "rlbox.wasm.h"
+#  define RLBOX_USE_STATIC_CALLS() rlbox_wasm2c_sandbox_lookup_symbol
+#  include "mozilla/rlbox/rlbox_wasm2c_sandbox.hpp"
+#else
+#  define RLBOX_USE_STATIC_CALLS() rlbox_noop_sandbox_lookup_symbol
+#  include "mozilla/rlbox/rlbox_noop_sandbox.hpp"
+#endif
+
+#include "mozilla/rlbox/rlbox.hpp"
+
+#include <hunspell.h>
+#include "mozHunspellRLBoxGlue.h"
+
+class RLBoxHunspell {
+ public:
+  static RLBoxHunspell* Create(const nsCString& affpath,
+                               const nsCString& dpath);
+
+  ~RLBoxHunspell();
+
+  int spell(const std::string& stdWord);
+  const std::string& get_dict_encoding() const;
+
+  std::vector<std::string> suggest(const std::string& word);
+
+ private:
+  struct RLBoxDeleter {
+    void operator()(rlbox_sandbox_hunspell* sandbox) {
+      sandbox->destroy_sandbox();
+      delete sandbox;
+    }
+  };
+
+  RLBoxHunspell(
+      mozilla::UniquePtr<rlbox_sandbox_hunspell, RLBoxDeleter> aSandbox,
+      const nsCString& affpath, const nsCString& dpath);
+
+  mozilla::UniquePtr<rlbox_sandbox_hunspell, RLBoxDeleter> mSandbox;
+  sandbox_callback_hunspell<hunspell_create_filemgr_t*> mCreateFilemgr;
+  sandbox_callback_hunspell<hunspell_get_line_t*> mGetLine;
+  sandbox_callback_hunspell<hunspell_get_line_num_t*> mGetLineNum;
+  sandbox_callback_hunspell<hunspell_destruct_filemgr_t*> mDestructFilemgr;
+  sandbox_callback_hunspell<hunspell_ToUpperCase_t*> mHunspellToUpperCase;
+  sandbox_callback_hunspell<hunspell_ToLowerCase_t*> mHunspellToLowerCase;
+  sandbox_callback_hunspell<hunspell_get_current_cs_t*> mHunspellGetCurrentCS;
+  tainted_hunspell<Hunhandle*> mHandle;
+  std::string mDicEncoding;
+};
+
+#endif
diff --git a/extensions/spellcheck/hunspell/glue/RLBoxHunspellTypes.h b/extensions/spellcheck/hunspell/glue/RLBoxHunspellTypes.h
new file mode 100644
index 0000000000..d05703ad0f
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/RLBoxHunspellTypes.h
@@ -0,0 +1,27 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 EXTENSIONS_SPELLCHECK_HUNSPELL_GLUE_RLBOXHUNSPELLTYPES_H_
+#define EXTENSIONS_SPELLCHECK_HUNSPELL_GLUE_RLBOXHUNSPELLTYPES_H_
+
+#include <stddef.h>
+#include "mozilla/rlbox/rlbox_types.hpp"
+#include "hunspell_csutil.hxx"
+
+#ifdef MOZ_WASM_SANDBOXING_HUNSPELL
+RLBOX_DEFINE_BASE_TYPES_FOR(hunspell, wasm2c)
+#else
+RLBOX_DEFINE_BASE_TYPES_FOR(hunspell, noop)
+#endif
+
+#define sandbox_fields_reflection_hunspell_class_cs_info(f, g, ...) \
+  f(unsigned char, ccase, FIELD_NORMAL, ##__VA_ARGS__) g()          \
+      f(unsigned char, clower, FIELD_NORMAL, ##__VA_ARGS__) g()     \
+          f(unsigned char, cupper, FIELD_NORMAL, ##__VA_ARGS__) g()
+
+#define sandbox_fields_reflection_hunspell_allClasses(f, ...) \
+  f(cs_info, hunspell, ##__VA_ARGS__)
+
+#endif
diff --git a/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.cpp b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.cpp
new file mode 100644
index 0000000000..8971694db3
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.cpp
@@ -0,0 +1,84 @@
+/* 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 "mozilla/UniquePtr.h"
+#include "RemoteSpellCheckEngineChild.h"
+
+namespace mozilla {
+
+RemoteSpellcheckEngineChild::RemoteSpellcheckEngineChild(
+    mozSpellChecker* aOwner)
+    : mOwner(aOwner) {}
+
+RemoteSpellcheckEngineChild::~RemoteSpellcheckEngineChild() {
+  // null out the owner's SpellcheckEngineChild to prevent state corruption
+  // during shutdown
+  mOwner->DeleteRemoteEngine();
+}
+
+RefPtr<GenericPromise> RemoteSpellcheckEngineChild::SetCurrentDictionaries(
+    const nsTArray<nsCString>& aDictionaries) {
+  RefPtr<mozSpellChecker> spellChecker = mOwner;
+
+  return SendSetDictionaries(aDictionaries)
+      ->Then(
+          GetMainThreadSerialEventTarget(), __func__,
+          [spellChecker, dictionaries = aDictionaries.Clone()](bool&& aParam) {
+            if (aParam) {
+              spellChecker->mCurrentDictionaries = dictionaries.Clone();
+              return GenericPromise::CreateAndResolve(true, __func__);
+            }
+            spellChecker->mCurrentDictionaries.Clear();
+            return GenericPromise::CreateAndReject(NS_ERROR_NOT_AVAILABLE,
+                                                   __func__);
+          },
+          [spellChecker](ResponseRejectReason&& aReason) {
+            spellChecker->mCurrentDictionaries.Clear();
+            return GenericPromise::CreateAndReject(NS_ERROR_NOT_AVAILABLE,
+                                                   __func__);
+          });
+}
+
+RefPtr<GenericPromise>
+RemoteSpellcheckEngineChild::SetCurrentDictionaryFromList(
+    const nsTArray<nsCString>& aList) {
+  RefPtr<mozSpellChecker> spellChecker = mOwner;
+
+  return SendSetDictionaryFromList(aList)->Then(
+      GetMainThreadSerialEventTarget(), __func__,
+      [spellChecker](std::tuple<bool, nsCString>&& aParam) {
+        if (!std::get<0>(aParam)) {
+          spellChecker->mCurrentDictionaries.Clear();
+          return GenericPromise::CreateAndReject(NS_ERROR_NOT_AVAILABLE,
+                                                 __func__);
+        }
+        spellChecker->mCurrentDictionaries.Clear();
+        spellChecker->mCurrentDictionaries.AppendElement(
+            std::move(std::get<1>(aParam)));
+        return GenericPromise::CreateAndResolve(true, __func__);
+      },
+      [spellChecker](ResponseRejectReason&& aReason) {
+        spellChecker->mCurrentDictionaries.Clear();
+        return GenericPromise::CreateAndReject(NS_ERROR_NOT_AVAILABLE,
+                                               __func__);
+      });
+}
+
+RefPtr<CheckWordPromise> RemoteSpellcheckEngineChild::CheckWords(
+    const nsTArray<nsString>& aWords) {
+  RefPtr<mozSpellChecker> kungFuDeathGrip = mOwner;
+
+  return SendCheckAsync(aWords)->Then(
+      GetMainThreadSerialEventTarget(), __func__,
+      [kungFuDeathGrip](nsTArray<bool>&& aIsMisspelled) {
+        return CheckWordPromise::CreateAndResolve(std::move(aIsMisspelled),
+                                                  __func__);
+      },
+      [kungFuDeathGrip](mozilla::ipc::ResponseRejectReason&& aReason) {
+        return CheckWordPromise::CreateAndReject(NS_ERROR_NOT_AVAILABLE,
+                                                 __func__);
+      });
+}
+
+}  // namespace mozilla
diff --git a/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.h b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.h
new file mode 100644
index 0000000000..06721d91ea
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.h
@@ -0,0 +1,36 @@
+/* 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 RemoteSpellcheckEngineChild_h_
+#define RemoteSpellcheckEngineChild_h_
+
+#include "mozilla/MozPromise.h"
+#include "mozilla/PRemoteSpellcheckEngineChild.h"
+#include "mozSpellChecker.h"
+
+class mozSpellChecker;
+
+namespace mozilla {
+
+class RemoteSpellcheckEngineChild
+    : public mozilla::PRemoteSpellcheckEngineChild {
+ public:
+  explicit RemoteSpellcheckEngineChild(mozSpellChecker* aOwner);
+  virtual ~RemoteSpellcheckEngineChild();
+
+  RefPtr<GenericPromise> SetCurrentDictionaries(
+      const nsTArray<nsCString>& aDictionaries);
+
+  RefPtr<GenericPromise> SetCurrentDictionaryFromList(
+      const nsTArray<nsCString>& aList);
+
+  RefPtr<CheckWordPromise> CheckWords(const nsTArray<nsString>& aWords);
+
+ private:
+  mozSpellChecker* mOwner;
+};
+
+}  // namespace mozilla
+
+#endif  // RemoteSpellcheckEngineChild_h_
diff --git a/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineParent.cpp b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineParent.cpp
new file mode 100644
index 0000000000..e9f341d524
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineParent.cpp
@@ -0,0 +1,85 @@
+/* vim: set ts=2 sw=2 sts=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 "RemoteSpellCheckEngineParent.h"
+#include "mozilla/Unused.h"
+#include "mozilla/mozSpellChecker.h"
+#include "nsServiceManagerUtils.h"
+
+namespace mozilla {
+
+RemoteSpellcheckEngineParent::RemoteSpellcheckEngineParent() {
+  mSpellChecker = mozSpellChecker::Create();
+}
+
+RemoteSpellcheckEngineParent::~RemoteSpellcheckEngineParent() {}
+
+mozilla::ipc::IPCResult RemoteSpellcheckEngineParent::RecvSetDictionary(
+    const nsACString& aDictionary, bool* success) {
+  nsresult rv = mSpellChecker->SetCurrentDictionary(aDictionary);
+  *success = NS_SUCCEEDED(rv);
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult RemoteSpellcheckEngineParent::RecvSetDictionaries(
+    const nsTArray<nsCString>& aDictionaries,
+    SetDictionariesResolver&& aResolve) {
+  mSpellChecker->SetCurrentDictionaries(aDictionaries)
+      ->Then(
+          GetMainThreadSerialEventTarget(), __func__,
+          [aResolve]() { aResolve(true); }, [aResolve]() { aResolve(false); });
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult RemoteSpellcheckEngineParent::RecvSetDictionaryFromList(
+    nsTArray<nsCString>&& aList, SetDictionaryFromListResolver&& aResolve) {
+  for (auto& dictionary : aList) {
+    nsresult rv = mSpellChecker->SetCurrentDictionary(dictionary);
+    if (NS_SUCCEEDED(rv)) {
+      aResolve(std::tuple<const bool&, const nsACString&>(true, dictionary));
+      return IPC_OK();
+    }
+  }
+  aResolve(std::tuple<const bool&, const nsACString&>(false, ""_ns));
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult RemoteSpellcheckEngineParent::RecvCheckAsync(
+    nsTArray<nsString>&& aWords, CheckAsyncResolver&& aResolve) {
+  nsTArray<bool> misspells;
+  misspells.SetCapacity(aWords.Length());
+  for (auto& word : aWords) {
+    bool misspelled;
+    nsresult rv = mSpellChecker->CheckWord(word, &misspelled, nullptr);
+    // If CheckWord failed, we can't tell whether the word is correctly spelled
+    if (NS_FAILED(rv)) {
+      misspelled = false;
+    }
+    misspells.AppendElement(misspelled);
+  }
+  aResolve(std::move(misspells));
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult RemoteSpellcheckEngineParent::RecvSuggest(
+    const nsAString& aWord, uint32_t aCount, SuggestResolver&& aResolve) {
+  nsTArray<nsString> suggestions;
+  mSpellChecker->Suggest(aWord, aCount)
+      ->Then(
+          GetMainThreadSerialEventTarget(), __func__,
+          [aResolve](CopyableTArray<nsString> aSuggestions) {
+            aResolve(std::move(aSuggestions));
+          },
+          [aResolve](nsresult aError) {
+            // No suggestions due to error
+            nsTArray<nsString> suggestions;
+            aResolve(std::move(suggestions));
+          });
+  return IPC_OK();
+}
+
+void RemoteSpellcheckEngineParent::ActorDestroy(ActorDestroyReason aWhy) {}
+
+}  // namespace mozilla
diff --git a/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineParent.h b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineParent.h
new file mode 100644
index 0000000000..06f4a7e8f5
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineParent.h
@@ -0,0 +1,46 @@
+/* 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 RemoteSpellcheckEngineParent_h_
+#define RemoteSpellcheckEngineParent_h_
+
+#include "mozilla/PRemoteSpellcheckEngineParent.h"
+#include "nsCOMPtr.h"
+#include "nsTArray.h"
+
+class mozSpellChecker;
+
+namespace mozilla {
+
+class RemoteSpellcheckEngineParent : public PRemoteSpellcheckEngineParent {
+ public:
+  RemoteSpellcheckEngineParent();
+
+  virtual ~RemoteSpellcheckEngineParent();
+
+  virtual void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  virtual mozilla::ipc::IPCResult RecvSetDictionary(
+      const nsACString& aDictionary, bool* success);
+
+  virtual mozilla::ipc::IPCResult RecvSetDictionaries(
+      const nsTArray<nsCString>& aDictionaries,
+      SetDictionariesResolver&& aResolve);
+
+  virtual mozilla::ipc::IPCResult RecvSetDictionaryFromList(
+      nsTArray<nsCString>&& aList, SetDictionaryFromListResolver&& aResolve);
+
+  virtual mozilla::ipc::IPCResult RecvCheckAsync(nsTArray<nsString>&& aWord,
+                                                 CheckAsyncResolver&& aResolve);
+
+  virtual mozilla::ipc::IPCResult RecvSuggest(const nsAString& aWord,
+                                              uint32_t aCount,
+                                              SuggestResolver&& aResolve);
+
+ private:
+  RefPtr<mozSpellChecker> mSpellChecker;
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/extensions/spellcheck/hunspell/glue/common.mozbuild b/extensions/spellcheck/hunspell/glue/common.mozbuild
new file mode 100644
index 0000000000..ded414075e
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/common.mozbuild
@@ -0,0 +1,9 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+@template
+def HunspellIncludes():
+    ForceInclude('hunspell_alloc_hooks.h', 'hunspell_fopen_hooks.h')
diff --git a/extensions/spellcheck/hunspell/glue/hunspell_alloc_hooks.h b/extensions/spellcheck/hunspell/glue/hunspell_alloc_hooks.h
new file mode 100644
index 0000000000..27a719d788
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/hunspell_alloc_hooks.h
@@ -0,0 +1,59 @@
+/******* BEGIN LICENSE BLOCK *******
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Initial Developers of the Original Code is Mozilla Foundation.
+ * Portions created by the Initial Developers
+ * are Copyright (C) 2011 the Initial Developers. All Rights Reserved.
+ *
+ * Contributor(s):
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ ******* END LICENSE BLOCK *******/
+
+#ifndef alloc_hooks_h__
+#define alloc_hooks_h__
+
+/**
+ * This file is force-included in hunspell code.  Its purpose is to add memory
+ * reporting to hunspell without modifying its code, in order to ease future
+ * upgrades.
+ *
+ * Currently, the memory allocated using operator new/new[] is not being
+ * tracked, but that's OK, since almost all of the memory used by Hunspell is
+ * allocated using C memory allocation functions.
+ */
+
+#include "mozHunspellAllocator.h"
+
+// Ensure that malloc is imported before we set our malloc-counting hooks below.
+// Otherwise, if malloc is imported afterwards, its source will be trampled
+// over by the "#define"s.
+#include "mozmemory.h"
+
+#define malloc(size) HunspellAllocator::CountingMalloc(size)
+#define calloc(count, size) HunspellAllocator::CountingCalloc(count, size)
+#define free(ptr) HunspellAllocator::CountingFree(ptr)
+#define realloc(ptr, size) HunspellAllocator::CountingRealloc(ptr, size)
+
+#endif
diff --git a/extensions/spellcheck/hunspell/glue/hunspell_csutil.cxx b/extensions/spellcheck/hunspell/glue/hunspell_csutil.cxx
new file mode 100644
index 0000000000..0f5565a12c
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/hunspell_csutil.cxx
@@ -0,0 +1,160 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * Copyright (C) 2002-2017 Németh László
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * Hunspell is based on MySpell which is Copyright (C) 2002 Kevin Hendricks.
+ *
+ * Contributor(s): David Einstein, Davide Prina, Giuseppe Modugno,
+ * Gianluca Turconi, Simon Brouwer, Noll János, Bíró Árpád,
+ * Goldman Eleonóra, Sarlós Tamás, Bencsáth Boldizsár, Halácsy Péter,
+ * Dvornik László, Gefferth András, Nagy Viktor, Varga Dániel, Chris Halls,
+ * Rene Engelhard, Bram Moolenaar, Dafydd Jones, Harri Pitkänen
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+/*
+ * Copyright 2002 Kevin B. Hendricks, Stratford, Ontario, Canada
+ * And Contributors.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * 3. All modifications to the source code must be clearly marked as
+ *    such.  Binary redistributions based on modified source code
+ *    must be clearly marked as modified versions in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY KEVIN B. HENDRICKS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
+ * KEVIN B. HENDRICKS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+#include "hunspell_csutil.hxx"
+#include "mozilla/Encoding.h"
+#include "mozilla/Span.h"
+#include "nsUnicharUtils.h"
+
+/* This is a copy of get_current_cs from the hunspell csutil.cxx file.
+ */
+struct cs_info* hunspell_get_current_cs(const std::string& es) {
+  struct cs_info* ccs = new cs_info[256];
+  // Initialze the array with dummy data so that we wouldn't need
+  // to return null in case of failures.
+  for (int i = 0; i <= 0xff; ++i) {
+    ccs[i].ccase = false;
+    ccs[i].clower = i;
+    ccs[i].cupper = i;
+  }
+
+  auto encoding = mozilla::Encoding::ForLabelNoReplacement(es);
+  if (!encoding) {
+    return ccs;
+  }
+  auto encoder = encoding->NewEncoder();
+  auto decoder = encoding->NewDecoderWithoutBOMHandling();
+
+  for (unsigned int i = 0; i <= 0xff; ++i) {
+    bool success = false;
+    // We want to find the upper/lowercase equivalents of each byte
+    // in this 1-byte character encoding.  Call our encoding/decoding
+    // APIs separately for each byte since they may reject some of the
+    // bytes, and we want to handle errors separately for each byte.
+    uint8_t lower, upper;
+    do {
+      if (i == 0) break;
+      uint8_t source = uint8_t(i);
+      char16_t uni[2];
+      char16_t uniCased;
+      uint8_t destination[4];
+      auto src1 = mozilla::Span(&source, 1);
+      auto dst1 = mozilla::Span(uni);
+      auto src2 = mozilla::Span(&uniCased, 1);
+      auto dst2 = mozilla::Span(destination);
+
+      uint32_t result;
+      size_t read;
+      size_t written;
+      std::tie(result, read, written) =
+          decoder->DecodeToUTF16WithoutReplacement(src1, dst1, true);
+      if (result != mozilla::kInputEmpty || read != 1 || written != 1) {
+        break;
+      }
+
+      uniCased = ToLowerCase(uni[0]);
+      std::tie(result, read, written) =
+          encoder->EncodeFromUTF16WithoutReplacement(src2, dst2, true);
+      if (result != mozilla::kInputEmpty || read != 1 || written != 1) {
+        break;
+      }
+      lower = destination[0];
+
+      uniCased = ToUpperCase(uni[0]);
+      std::tie(result, read, written) =
+          encoder->EncodeFromUTF16WithoutReplacement(src2, dst2, true);
+      if (result != mozilla::kInputEmpty || read != 1 || written != 1) {
+        break;
+      }
+      upper = destination[0];
+
+      success = true;
+    } while (0);
+
+    encoding->NewEncoderInto(*encoder);
+    encoding->NewDecoderWithoutBOMHandlingInto(*decoder);
+
+    if (success) {
+      ccs[i].cupper = upper;
+      ccs[i].clower = lower;
+    } else {
+      ccs[i].cupper = i;
+      ccs[i].clower = i;
+    }
+
+    if (ccs[i].clower != (unsigned char)i)
+      ccs[i].ccase = true;
+    else
+      ccs[i].ccase = false;
+  }
+
+  return ccs;
+}
diff --git a/extensions/spellcheck/hunspell/glue/hunspell_csutil.hxx b/extensions/spellcheck/hunspell/glue/hunspell_csutil.hxx
new file mode 100644
index 0000000000..00dd89a964
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/hunspell_csutil.hxx
@@ -0,0 +1,87 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * Copyright (C) 2002-2017 Németh László
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * Hunspell is based on MySpell which is Copyright (C) 2002 Kevin Hendricks.
+ *
+ * Contributor(s): David Einstein, Davide Prina, Giuseppe Modugno,
+ * Gianluca Turconi, Simon Brouwer, Noll János, Bíró Árpád,
+ * Goldman Eleonóra, Sarlós Tamás, Bencsáth Boldizsár, Halácsy Péter,
+ * Dvornik László, Gefferth András, Nagy Viktor, Varga Dániel, Chris Halls,
+ * Rene Engelhard, Bram Moolenaar, Dafydd Jones, Harri Pitkänen
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+/*
+ * Copyright 2002 Kevin B. Hendricks, Stratford, Ontario, Canada
+ * And Contributors.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * 3. All modifications to the source code must be clearly marked as
+ *    such.  Binary redistributions based on modified source code
+ *    must be clearly marked as modified versions in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY KEVIN B. HENDRICKS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
+ * KEVIN B. HENDRICKS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+#ifndef EXTENSIONS_SPELLCHECK_HUNSPELL_GLUE_HUNSPELL_CSUTIL_H_
+#define EXTENSIONS_SPELLCHECK_HUNSPELL_GLUE_HUNSPELL_CSUTIL_H_
+
+/* We need get_current_cs from hunspell's csutil to live outside the RLBox
+ * sandbox (since it relies on a Gecko encoding bits) and then expose it to the
+ * sandboxed hunspell.
+ */
+
+struct cs_info {
+  unsigned char ccase;
+  unsigned char clower;
+  unsigned char cupper;
+};
+
+struct cs_info* hunspell_get_current_cs(const std::string& es);
+
+#endif
diff --git a/extensions/spellcheck/hunspell/glue/hunspell_fopen_hooks.h b/extensions/spellcheck/hunspell/glue/hunspell_fopen_hooks.h
new file mode 100644
index 0000000000..7388b1daa7
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/hunspell_fopen_hooks.h
@@ -0,0 +1,81 @@
+/* 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 fopen_hooks_h__
+#define fopen_hooks_h__
+
+/**
+ * This file is force-included in hunspell code. Its purpose is to add
+ * readahead to fopen() calls in hunspell without modifying its code, in order
+ * to ease future upgrades.
+ */
+
+#include "mozilla/FileUtils.h"
+#include <stdio.h>
+#include <string.h>
+
+#if defined(XP_WIN)
+#  include "nsNativeCharsetUtils.h"
+#  include "nsString.h"
+
+#  include <fcntl.h>
+#  include <windows.h>
+// Hunspell defines a function named near. Windef.h #defines near.
+#  undef near
+// mozHunspell defines a function named RemoveDirectory.
+#  undef RemoveDirectory
+#endif /* defined(XP_WIN) */
+
+inline FILE* hunspell_fopen_readahead(const char* filename, const char* mode) {
+  if (!filename || !mode) {
+    return nullptr;
+  }
+  // Fall back to libc's fopen for modes not supported by ReadAheadFile
+  if (!strchr(mode, 'r') || strchr(mode, '+')) {
+    return fopen(filename, mode);
+  }
+  int fd = -1;
+#if defined(XP_WIN)
+  // filename is obtained via the nsIFile::nativePath attribute, so
+  // it is using the Windows ANSI code page, NOT UTF-8!
+  nsAutoString utf16Filename;
+  nsresult rv =
+      NS_CopyNativeToUnicode(nsDependentCString(filename), utf16Filename);
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+  HANDLE handle = INVALID_HANDLE_VALUE;
+  mozilla::ReadAheadFile(utf16Filename.get(), 0, SIZE_MAX, &handle);
+  if (handle == INVALID_HANDLE_VALUE) {
+    return nullptr;
+  }
+  int flags = _O_RDONLY;
+  // MSVC CRT's _open_osfhandle only supports adding _O_TEXT, not _O_BINARY
+  if (strchr(mode, 't')) {
+    // Force translated mode
+    flags |= _O_TEXT;
+  }
+  // Import the Win32 fd into the CRT
+  fd = _open_osfhandle((intptr_t)handle, flags);
+  if (fd < 0) {
+    CloseHandle(handle);
+    return nullptr;
+  }
+#else
+  mozilla::ReadAheadFile(filename, 0, SIZE_MAX, &fd);
+  if (fd < 0) {
+    return nullptr;
+  }
+#endif /* defined(XP_WIN) */
+
+  FILE* file = fdopen(fd, mode);
+  if (!file) {
+    close(fd);
+  }
+  return file;
+}
+
+#define fopen(filename, mode) hunspell_fopen_readahead(filename, mode)
+
+#endif /* fopen_hooks_h__ */
diff --git a/extensions/spellcheck/hunspell/glue/moz.build b/extensions/spellcheck/hunspell/glue/moz.build
new file mode 100644
index 0000000000..7cde4156c7
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/moz.build
@@ -0,0 +1,39 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+UNIFIED_SOURCES += [
+    "hunspell_csutil.cxx",
+    "mozHunspell.cpp",
+    "mozHunspellRLBoxHost.cpp",
+    "RemoteSpellCheckEngineChild.cpp",
+    "RemoteSpellCheckEngineParent.cpp",
+    "RLBoxHunspell.cpp",
+]
+
+DEFINES["HUNSPELL_STATIC"] = True
+
+FINAL_LIBRARY = "xul"
+
+LOCAL_INCLUDES += [
+    "!/security/rlbox",
+    "../src",
+    "/dom/base",
+    "/extensions/spellcheck/src",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+include("common.mozbuild")
+
+HunspellIncludes()
+
+IPDL_SOURCES = [
+    "PRemoteSpellcheckEngine.ipdl",
+]
+
+EXPORTS.mozilla += [
+    "RemoteSpellCheckEngineChild.h",
+    "RemoteSpellCheckEngineParent.h",
+]
diff --git a/extensions/spellcheck/hunspell/glue/mozHunspell.cpp b/extensions/spellcheck/hunspell/glue/mozHunspell.cpp
new file mode 100644
index 0000000000..a69dcd6b05
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspell.cpp
@@ -0,0 +1,594 @@
+/******* BEGIN LICENSE BLOCK *******
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Initial Developers of the Original Code are Kevin Hendricks (MySpell)
+ * and László Németh (Hunspell). Portions created by the Initial Developers
+ * are Copyright (C) 2002-2005 the Initial Developers. All Rights Reserved.
+ *
+ * Contributor(s): Kevin Hendricks (kevin.hendricks@sympatico.ca)
+ *                 David Einstein (deinst@world.std.com)
+ *                 Michiel van Leeuwen (mvl@exedo.nl)
+ *                 Caolan McNamara (cmc@openoffice.org)
+ *                 László Németh (nemethl@gyorsposta.hu)
+ *                 Davide Prina
+ *                 Giuseppe Modugno
+ *                 Gianluca Turconi
+ *                 Simon Brouwer
+ *                 Noll Janos
+ *                 Biro Arpad
+ *                 Goldman Eleonora
+ *                 Sarlos Tamas
+ *                 Bencsath Boldizsar
+ *                 Halacsy Peter
+ *                 Dvornik Laszlo
+ *                 Gefferth Andras
+ *                 Nagy Viktor
+ *                 Varga Daniel
+ *                 Chris Halls
+ *                 Rene Engelhard
+ *                 Bram Moolenaar
+ *                 Dafydd Jones
+ *                 Harri Pitkanen
+ *                 Andras Timar
+ *                 Tor Lillqvist
+ *                 Jesper Kristensen (mail@jesperkristensen.dk)
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ ******* END LICENSE BLOCK *******/
+
+#include "mozHunspell.h"
+#include "nsReadableUtils.h"
+#include "nsString.h"
+#include "nsIObserverService.h"
+#include "nsIDirectoryEnumerator.h"
+#include "nsIFile.h"
+#include "nsUnicharUtils.h"
+#include "nsCRT.h"
+#include "mozInlineSpellChecker.h"
+#include "nsIPrefBranch.h"
+#include "nsIPrefService.h"
+#include "nsNetUtil.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/Components.h"
+#include "mozilla/Services.h"
+
+#include <stdlib.h>
+#include <tuple>
+
+using mozilla::dom::ContentParent;
+using namespace mozilla;
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(mozHunspell)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(mozHunspell)
+
+NS_INTERFACE_MAP_BEGIN(mozHunspell)
+  NS_INTERFACE_MAP_ENTRY(mozISpellCheckingEngine)
+  NS_INTERFACE_MAP_ENTRY(nsIObserver)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+  NS_INTERFACE_MAP_ENTRY(nsIMemoryReporter)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozISpellCheckingEngine)
+  NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(mozHunspell)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION_WEAK(mozHunspell, mPersonalDictionary)
+
+NS_IMPL_COMPONENT_FACTORY(mozHunspell) {
+  auto hunspell = MakeRefPtr<mozHunspell>();
+  if (NS_SUCCEEDED(hunspell->Init())) {
+    return hunspell.forget().downcast<mozISpellCheckingEngine>();
+  }
+  return nullptr;
+}
+
+mozHunspell::mozHunspell() {
+#ifdef DEBUG
+  // There must be only one instance of this class: it reports memory based on
+  // a single static count in HunspellAllocator.
+  static bool hasRun = false;
+  MOZ_ASSERT(!hasRun);
+  hasRun = true;
+#endif
+}
+
+nsresult mozHunspell::Init() {
+  LoadDictionaryList(false);
+
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    obs->AddObserver(this, "profile-do-change", true);
+    obs->AddObserver(this, "profile-after-change", true);
+  }
+
+  mozilla::RegisterWeakMemoryReporter(this);
+
+  return NS_OK;
+}
+
+mozHunspell::~mozHunspell() {
+  mozilla::UnregisterWeakMemoryReporter(this);
+
+  mPersonalDictionary = nullptr;
+  mHunspells.Clear();
+}
+
+NS_IMETHODIMP
+mozHunspell::GetDictionaries(nsTArray<nsCString>& aDictionaries) {
+  MOZ_ASSERT(aDictionaries.IsEmpty());
+  for (auto iter = mHunspells.ConstIter(); !iter.Done(); iter.Next()) {
+    if (iter.Data().mEnabled) {
+      aDictionaries.AppendElement(iter.Key());
+    }
+  }
+  return NS_OK;
+}
+
+/* Set the Dictionaries.
+ * This also Loads the dictionaries and initializes the converter using the
+ * dictionaries converter
+ */
+NS_IMETHODIMP
+mozHunspell::SetDictionaries(const nsTArray<nsCString>& aDictionaries) {
+  if (aDictionaries.IsEmpty()) {
+    mHunspells.Clear();
+    return NS_OK;
+  }
+
+  // Disable any dictionaries we've already loaded that we're not
+  // going to use.
+  for (auto iter = mHunspells.Iter(); !iter.Done(); iter.Next()) {
+    if (!aDictionaries.Contains(iter.Key())) {
+      iter.Data().mEnabled = false;
+    }
+  }
+
+  bool firstDictionary = true;
+  for (const auto& dictionary : aDictionaries) {
+    NS_ConvertUTF8toUTF16 dict(dictionary);
+    nsIURI* affFile = mDictionaries.GetWeak(dict);
+    if (!affFile) {
+      return NS_ERROR_FILE_NOT_FOUND;
+    }
+
+    nsAutoCString affFileName;
+    nsresult rv = affFile->GetSpec(affFileName);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (auto entry = mHunspells.Lookup(dictionary)) {
+      if (entry.Data().mAffixFileName == affFileName) {
+        entry.Data().mEnabled = true;
+        continue;
+      }
+    }
+
+    DictionaryData dictionaryData;
+    dictionaryData.mAffixFileName = affFileName;
+
+    // Load the first dictionary now, we'll load the others lazily during
+    // checking.
+    if (firstDictionary) {
+      rv = dictionaryData.LoadIfNecessary();
+      NS_ENSURE_SUCCESS(rv, rv);
+      firstDictionary = false;
+    }
+
+    mHunspells.InsertOrUpdate(dictionary, std::move(dictionaryData));
+  }
+
+  // If we have a large number of dictionaries loaded, try freeing any disabled
+  // dictionaries to limit memory use.
+  if (mHunspells.Count() > 10) {
+    mHunspells.RemoveIf([](const auto& iter) { return !iter.Data().mEnabled; });
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP mozHunspell::GetPersonalDictionary(
+    mozIPersonalDictionary** aPersonalDictionary) {
+  *aPersonalDictionary = mPersonalDictionary;
+  NS_IF_ADDREF(*aPersonalDictionary);
+  return NS_OK;
+}
+
+NS_IMETHODIMP mozHunspell::SetPersonalDictionary(
+    mozIPersonalDictionary* aPersonalDictionary) {
+  mPersonalDictionary = aPersonalDictionary;
+  return NS_OK;
+}
+
+NS_IMETHODIMP mozHunspell::GetDictionaryList(
+    nsTArray<nsCString>& aDictionaries) {
+  MOZ_ASSERT(aDictionaries.IsEmpty());
+  for (const auto& key : mDictionaries.Keys()) {
+    aDictionaries.AppendElement(NS_ConvertUTF16toUTF8(key));
+  }
+
+  return NS_OK;
+}
+
+void mozHunspell::LoadDictionaryList(bool aNotifyChildProcesses) {
+  mDictionaries.Clear();
+
+  nsresult rv;
+
+  // find built in dictionaries, or dictionaries specified in
+  // spellchecker.dictionary_path in prefs
+  nsCOMPtr<nsIFile> dictDir;
+
+  // check preferences first
+  nsCOMPtr<nsIPrefBranch> prefs(do_GetService(NS_PREFSERVICE_CONTRACTID));
+  if (prefs) {
+    nsAutoCString extDictPath;
+    rv = prefs->GetCharPref("spellchecker.dictionary_path", extDictPath);
+    if (NS_SUCCEEDED(rv)) {
+      // set the spellchecker.dictionary_path
+      rv = NS_NewNativeLocalFile(extDictPath, true, getter_AddRefs(dictDir));
+    }
+    if (dictDir) {
+      LoadDictionariesFromDir(dictDir);
+    }
+  }
+
+  // find dictionaries in DICPATH
+  char* dicEnv = PR_GetEnv("DICPATH");
+  if (dicEnv) {
+    // do a two-pass dance so dictionaries are loaded right-to-left as
+    // preference
+    nsTArray<nsCOMPtr<nsIFile>> dirs;
+    nsAutoCString env(dicEnv);  // assume dicEnv is UTF-8
+
+    char* currPath = nullptr;
+    char* nextPaths = env.BeginWriting();
+    while ((currPath = NS_strtok(":", &nextPaths))) {
+      nsCOMPtr<nsIFile> dir;
+      rv =
+          NS_NewNativeLocalFile(nsCString(currPath), true, getter_AddRefs(dir));
+      if (NS_SUCCEEDED(rv)) {
+        dirs.AppendElement(dir);
+      }
+    }
+
+    // load them in reverse order so they override each other properly
+    for (int32_t i = dirs.Length() - 1; i >= 0; i--) {
+      LoadDictionariesFromDir(dirs[i]);
+    }
+  }
+
+  // find dictionaries from restartless extensions
+  for (int32_t i = 0; i < mDynamicDirectories.Count(); i++) {
+    LoadDictionariesFromDir(mDynamicDirectories[i]);
+  }
+
+  for (const auto& dictionaryEntry : mDynamicDictionaries) {
+    mDictionaries.InsertOrUpdate(dictionaryEntry.GetKey(),
+                                 dictionaryEntry.GetData());
+  }
+
+  DictionariesChanged(aNotifyChildProcesses);
+}
+
+void mozHunspell::DictionariesChanged(bool aNotifyChildProcesses) {
+  // Now we have finished updating the list of dictionaries, update the current
+  // dictionary and any editors which may use it.
+  mozInlineSpellChecker::UpdateCanEnableInlineSpellChecking();
+
+  if (aNotifyChildProcesses) {
+    ContentParent::NotifyUpdatedDictionaries();
+  }
+
+  // Check if the current dictionaries are still available.
+  // If not, try to replace it with other dictionaries of the same language.
+  if (!mHunspells.IsEmpty()) {
+    nsTArray<nsCString> dictionaries;
+    for (auto iter = mHunspells.ConstIter(); !iter.Done(); iter.Next()) {
+      if (iter.Data().mEnabled) {
+        dictionaries.AppendElement(iter.Key());
+      }
+    }
+    nsresult rv = SetDictionaries(dictionaries);
+    if (NS_SUCCEEDED(rv)) return;
+  }
+
+  // If the current dictionaries are gone, and we don't have a good replacement,
+  // set no current dictionary.
+  if (!mHunspells.IsEmpty()) {
+    nsTArray<nsCString> empty;
+    SetDictionaries(empty);
+  }
+}
+
+NS_IMETHODIMP
+mozHunspell::LoadDictionariesFromDir(nsIFile* aDir) {
+  nsresult rv;
+
+  bool check = false;
+  rv = aDir->Exists(&check);
+  if (NS_FAILED(rv) || !check) return NS_ERROR_UNEXPECTED;
+
+  rv = aDir->IsDirectory(&check);
+  if (NS_FAILED(rv) || !check) return NS_ERROR_UNEXPECTED;
+
+  nsCOMPtr<nsIDirectoryEnumerator> files;
+  rv = aDir->GetDirectoryEntries(getter_AddRefs(files));
+  if (NS_FAILED(rv)) return NS_ERROR_UNEXPECTED;
+
+  nsCOMPtr<nsIFile> file;
+  while (NS_SUCCEEDED(files->GetNextFile(getter_AddRefs(file))) && file) {
+    nsAutoString leafName;
+    file->GetLeafName(leafName);
+    if (!StringEndsWith(leafName, u".dic"_ns)) continue;
+
+    nsAutoString dict(leafName);
+    dict.SetLength(dict.Length() - 4);  // magic length of ".dic"
+
+    // check for the presence of the .aff file
+    leafName = dict;
+    leafName.AppendLiteral(".aff");
+    file->SetLeafName(leafName);
+    rv = file->Exists(&check);
+    if (NS_FAILED(rv) || !check) continue;
+
+    // Replace '_' separator with '-'
+    dict.ReplaceChar('_', '-');
+
+    nsCOMPtr<nsIURI> uri;
+    rv = NS_NewFileURI(getter_AddRefs(uri), file);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    mDictionaries.InsertOrUpdate(dict, uri);
+  }
+
+  return NS_OK;
+}
+
+nsresult mozHunspell::DictionaryData::ConvertCharset(const nsAString& aStr,
+                                                     std::string& aDst) {
+  if (NS_WARN_IF(!mEncoder)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  auto src = Span(aStr.BeginReading(), aStr.Length());
+  CheckedInt<size_t> needed =
+      mEncoder->MaxBufferLengthFromUTF16WithoutReplacement(src.Length());
+  if (!needed.isValid()) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  aDst.resize(needed.value());
+
+  char* dstPtr = &aDst[0];
+  auto dst = Span(reinterpret_cast<uint8_t*>(dstPtr), needed.value());
+
+  uint32_t result;
+  size_t written;
+  std::tie(result, std::ignore, written) =
+      mEncoder->EncodeFromUTF16WithoutReplacement(src, dst, true);
+  MOZ_ASSERT(result != kOutputFull);
+  if (result != kInputEmpty) {
+    return NS_ERROR_UENC_NOMAPPING;
+  }
+  aDst.resize(written);
+  mEncoder->Encoding()->NewEncoderInto(*mEncoder);
+  return NS_OK;
+}
+
+nsresult mozHunspell::DictionaryData::LoadIfNecessary() {
+  if (mHunspell && mEncoder && mDecoder) {
+    return NS_OK;
+  }
+
+  if (mLoadFailed) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCString dictFileName = mAffixFileName;
+  int32_t dotPos = dictFileName.RFindChar('.');
+  if (dotPos == -1) {
+    mLoadFailed = true;
+    return NS_ERROR_FAILURE;
+  }
+  dictFileName.SetLength(dotPos);
+  dictFileName.AppendLiteral(".dic");
+
+  UniquePtr<RLBoxHunspell> hunspell(
+      RLBoxHunspell::Create(mAffixFileName, dictFileName));
+  if (!hunspell) {
+    mLoadFailed = true;
+    // TODO Bug 1788857: Verify error propagation in case of inaccessible file
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  mHunspell = std::move(hunspell);
+  auto encoding =
+      Encoding::ForLabelNoReplacement(mHunspell->get_dict_encoding());
+  if (!encoding) {
+    mLoadFailed = true;
+    return NS_ERROR_UCONV_NOCONV;
+  }
+  mEncoder = encoding->NewEncoder();
+  mDecoder = encoding->NewDecoderWithoutBOMHandling();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+mozHunspell::CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) {
+  MOZ_COLLECT_REPORT("explicit/spell-check", KIND_HEAP, UNITS_BYTES,
+                     HunspellAllocator::MemoryAllocated(),
+                     "Memory used by the spell-checking engine.");
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+mozHunspell::Check(const nsAString& aWord, bool* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  if (NS_WARN_IF(mHunspells.IsEmpty())) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aResult = true;
+  for (auto iter = mHunspells.Iter(); !iter.Done(); iter.Next()) {
+    if (!iter.Data().mEnabled) {
+      continue;
+    }
+
+    nsresult rv = iter.Data().LoadIfNecessary();
+    if (NS_FAILED(rv)) {
+      continue;
+    }
+
+    std::string charsetWord;
+    rv = iter.Data().ConvertCharset(aWord, charsetWord);
+    if (NS_FAILED(rv)) {
+      continue;
+    }
+
+    // Depending upon the encoding, we might end up with a string that begins
+    // with the null byte. Since the hunspell interface uses C-style strings,
+    // this appears like an empty string, and hunspell marks empty strings as
+    // spelled correctly. Skip these cases to allow another dictionary to have
+    // the chance to spellcheck them.
+    if (charsetWord.empty() || charsetWord[0] == 0) {
+      continue;
+    }
+
+    *aResult = iter.Data().mHunspell->spell(charsetWord);
+    if (*aResult) {
+      break;
+    }
+  }
+
+  if (!*aResult && mPersonalDictionary) {
+    return mPersonalDictionary->Check(aWord, aResult);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+mozHunspell::Suggest(const nsAString& aWord, nsTArray<nsString>& aSuggestions) {
+  if (NS_WARN_IF(mHunspells.IsEmpty())) {
+    return NS_ERROR_FAILURE;
+  }
+
+  MOZ_ASSERT(aSuggestions.IsEmpty());
+
+  for (auto iter = mHunspells.Iter(); !iter.Done(); iter.Next()) {
+    if (!iter.Data().mEnabled) {
+      continue;
+    }
+
+    nsresult rv = iter.Data().LoadIfNecessary();
+    if (NS_FAILED(rv)) {
+      continue;
+    }
+
+    std::string charsetWord;
+    rv = iter.Data().ConvertCharset(aWord, charsetWord);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    std::vector<std::string> suggestions =
+        iter.Data().mHunspell->suggest(charsetWord);
+    if (!suggestions.empty()) {
+      aSuggestions.SetCapacity(aSuggestions.Length() + suggestions.size());
+      for (Span<const char> charSrc : suggestions) {
+        // Convert the suggestion to utf16
+        auto src = AsBytes(charSrc);
+        nsresult rv =
+            iter.Data().mDecoder->Encoding()->DecodeWithoutBOMHandling(
+                src, *aSuggestions.AppendElement());
+        NS_ENSURE_SUCCESS(rv, rv);
+        iter.Data().mDecoder->Encoding()->NewDecoderWithoutBOMHandlingInto(
+            *iter.Data().mDecoder);
+      }
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+mozHunspell::Observe(nsISupports* aSubj, const char* aTopic,
+                     const char16_t* aData) {
+  NS_ASSERTION(!strcmp(aTopic, "profile-do-change") ||
+                   !strcmp(aTopic, "profile-after-change"),
+               "Unexpected observer topic");
+
+  LoadDictionaryList(false);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP mozHunspell::AddDirectory(nsIFile* aDir) {
+  mDynamicDirectories.AppendObject(aDir);
+  LoadDictionaryList(true);
+  return NS_OK;
+}
+
+NS_IMETHODIMP mozHunspell::RemoveDirectory(nsIFile* aDir) {
+  mDynamicDirectories.RemoveObject(aDir);
+  LoadDictionaryList(true);
+
+#ifdef MOZ_THUNDERBIRD
+  /*
+   * This notification is needed for Thunderbird. Thunderbird derives the
+   * dictionary from the document's "lang" attribute. If a dictionary is
+   * removed, we need to change the "lang" attribute.
+   */
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    obs->NotifyObservers(nullptr, SPELLCHECK_DICTIONARY_REMOVE_NOTIFICATION,
+                         nullptr);
+  }
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP mozHunspell::AddDictionary(const nsAString& aLang,
+                                         nsIURI* aFile) {
+  NS_ENSURE_TRUE(aFile, NS_ERROR_INVALID_ARG);
+
+  mDynamicDictionaries.InsertOrUpdate(aLang, aFile);
+  mDictionaries.InsertOrUpdate(aLang, aFile);
+  DictionariesChanged(true);
+  return NS_OK;
+}
+
+NS_IMETHODIMP mozHunspell::RemoveDictionary(const nsAString& aLang,
+                                            nsIURI* aFile, bool* aRetVal) {
+  NS_ENSURE_TRUE(aFile, NS_ERROR_INVALID_ARG);
+  *aRetVal = false;
+
+  nsCOMPtr<nsIURI> file = mDynamicDictionaries.Get(aLang);
+  bool equal;
+  if (file && NS_SUCCEEDED(file->Equals(aFile, &equal)) && equal) {
+    mDynamicDictionaries.Remove(aLang);
+    LoadDictionaryList(true);
+    *aRetVal = true;
+  }
+  return NS_OK;
+}
diff --git a/extensions/spellcheck/hunspell/glue/mozHunspell.h b/extensions/spellcheck/hunspell/glue/mozHunspell.h
new file mode 100644
index 0000000000..89a38d9e49
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspell.h
@@ -0,0 +1,145 @@
+/******* BEGIN LICENSE BLOCK *******
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Initial Developers of the Original Code are Kevin Hendricks (MySpell)
+ * and László Németh (Hunspell). Portions created by the Initial Developers
+ * are Copyright (C) 2002-2005 the Initial Developers. All Rights Reserved.
+ *
+ * Contributor(s): Kevin Hendricks (kevin.hendricks@sympatico.ca)
+ *                 David Einstein (deinst@world.std.com)
+ *                 Michiel van Leeuwen (mvl@exedo.nl)
+ *                 Caolan McNamara (cmc@openoffice.org)
+ *                 László Németh (nemethl@gyorsposta.hu)
+ *                 Davide Prina
+ *                 Giuseppe Modugno
+ *                 Gianluca Turconi
+ *                 Simon Brouwer
+ *                 Noll Janos
+ *                 Biro Arpad
+ *                 Goldman Eleonora
+ *                 Sarlos Tamas
+ *                 Bencsath Boldizsar
+ *                 Halacsy Peter
+ *                 Dvornik Laszlo
+ *                 Gefferth Andras
+ *                 Nagy Viktor
+ *                 Varga Daniel
+ *                 Chris Halls
+ *                 Rene Engelhard
+ *                 Bram Moolenaar
+ *                 Dafydd Jones
+ *                 Harri Pitkanen
+ *                 Andras Timar
+ *                 Tor Lillqvist
+ *                 Jesper Kristensen (mail@jesperkristensen.dk)
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ ******* END LICENSE BLOCK *******/
+
+#ifndef mozHunspell_h__
+#define mozHunspell_h__
+
+#include "RLBoxHunspell.h"
+#include "mozISpellCheckingEngine.h"
+#include "mozIPersonalDictionary.h"
+#include "nsString.h"
+#include "nsCOMPtr.h"
+#include "nsCOMArray.h"
+#include "nsHashKeys.h"
+#include "nsIMemoryReporter.h"
+#include "nsIObserver.h"
+#include "nsIURI.h"
+#include "mozilla/Encoding.h"
+#include "mozilla/UniquePtr.h"
+#include "nsInterfaceHashtable.h"
+#include "nsWeakReference.h"
+#include "nsTHashMap.h"
+#include "nsCycleCollectionParticipant.h"
+#include "mozHunspellAllocator.h"
+
+#define MOZ_HUNSPELL_CONTRACTID "@mozilla.org/spellchecker/engine;1"
+#define MOZ_HUNSPELL_CID                             \
+  /* 56c778e4-1bee-45f3-a689-886692a97fe7 */         \
+  {                                                  \
+    0x56c778e4, 0x1bee, 0x45f3, {                    \
+      0xa6, 0x89, 0x88, 0x66, 0x92, 0xa9, 0x7f, 0xe7 \
+    }                                                \
+  }
+
+class mozHunspell final : public mozISpellCheckingEngine,
+                          public nsIObserver,
+                          public nsSupportsWeakReference,
+                          public nsIMemoryReporter {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_MOZISPELLCHECKINGENGINE
+  NS_DECL_NSIOBSERVER
+  NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(mozHunspell, mozISpellCheckingEngine)
+
+  mozHunspell();
+
+  nsresult Init();
+
+  void LoadDictionaryList(bool aNotifyChildProcesses);
+
+  NS_DECL_NSIMEMORYREPORTER
+
+ protected:
+  virtual ~mozHunspell();
+
+  void DictionariesChanged(bool aNotifyChildProcesses);
+
+  nsCOMPtr<mozIPersonalDictionary> mPersonalDictionary;
+
+  // Hashtable matches dictionary name to .aff file
+  nsInterfaceHashtable<nsStringHashKey, nsIURI> mDictionaries;
+
+  // dynamic dirs used to search for dictionaries
+  nsCOMArray<nsIFile> mDynamicDirectories;
+  nsInterfaceHashtable<nsStringHashKey, nsIURI> mDynamicDictionaries;
+
+  struct DictionaryData {
+    // keep track of whether the dictionary is currently in use or not
+    bool mEnabled = true;
+
+    // keep track of whether we've failed loading this dictionary before.
+    // if set, we don't try loading it again.
+    bool mLoadFailed = false;
+
+    mozilla::UniquePtr<mozilla::Encoder> mEncoder;
+    mozilla::UniquePtr<mozilla::Decoder> mDecoder;
+    mozilla::UniquePtr<RLBoxHunspell> mHunspell;
+    nsCString mAffixFileName;
+
+    // helper method for converting a word to the charset of the dictionary
+    nsresult ConvertCharset(const nsAString& aStr, std::string& aDst);
+
+    // helper method to the load the dictionary if it is not already loaded
+    nsresult LoadIfNecessary();
+  };
+
+  nsTHashMap<nsCStringHashKey, DictionaryData> mHunspells;
+};
+
+#endif
diff --git a/extensions/spellcheck/hunspell/glue/mozHunspellAllocator.h b/extensions/spellcheck/hunspell/glue/mozHunspellAllocator.h
new file mode 100644
index 0000000000..ddcec3e28c
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspellAllocator.h
@@ -0,0 +1,15 @@
+/* -*- 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 mozHunspellAllocator_h__
+#define mozHunspellAllocator_h__
+
+#include "mozilla/CountingAllocatorBase.h"
+
+class HunspellAllocator
+    : public mozilla::CountingAllocatorBase<HunspellAllocator> {};
+
+#endif
diff --git a/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxGlue.h b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxGlue.h
new file mode 100644
index 0000000000..d84a5ba739
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxGlue.h
@@ -0,0 +1,45 @@
+/* -*- 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 mozHunspellRLBoxGlue_h
+#define mozHunspellRLBoxGlue_h
+
+#include <stdint.h>
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+typedef uint32_t(hunspell_create_filemgr_t)(const char* aFilename);
+typedef bool(hunspell_get_line_t)(uint32_t aFd, char** aLinePtr);
+typedef int(hunspell_get_line_num_t)(uint32_t aFd);
+typedef void(hunspell_destruct_filemgr_t)(uint32_t aFd);
+typedef uint32_t(hunspell_ToUpperCase_t)(uint32_t aChar);
+typedef uint32_t(hunspell_ToLowerCase_t)(uint32_t aChar);
+typedef struct cs_info*(hunspell_get_current_cs_t)(const char* es);
+
+void RegisterHunspellCallbacks(
+    hunspell_create_filemgr_t* aHunspellCreateFilemgr,
+    hunspell_get_line_t* aHunspellGetLine,
+    hunspell_get_line_num_t* aHunspellGetLine_num,
+    hunspell_destruct_filemgr_t* aHunspellDestructFilemgr,
+    hunspell_ToUpperCase_t* aHunspellToUpperCase,
+    hunspell_ToLowerCase_t* aHunspellToLowerCase,
+    hunspell_get_current_cs_t* aHunspellGetCurrentCS);
+
+extern hunspell_create_filemgr_t* moz_glue_hunspell_create_filemgr;
+extern hunspell_get_line_t* moz_glue_hunspell_get_line;
+extern hunspell_get_line_num_t* moz_glue_hunspell_get_line_num;
+extern hunspell_destruct_filemgr_t* moz_glue_hunspell_destruct_filemgr;
+extern hunspell_ToUpperCase_t* moz_hunspell_ToUpperCase;
+extern hunspell_ToLowerCase_t* moz_hunspell_ToLowerCase;
+extern hunspell_get_current_cs_t* moz_hunspell_GetCurrentCS;
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif
diff --git a/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxHost.cpp b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxHost.cpp
new file mode 100644
index 0000000000..cd80fb989b
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxHost.cpp
@@ -0,0 +1,235 @@
+/* -*- 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 <limits>
+
+#include "mozHunspellRLBoxHost.h"
+#include "mozilla/DebugOnly.h"
+#include "nsContentUtils.h"
+#include "nsILoadInfo.h"
+#include "nsNetUtil.h"
+#include "nsUnicharUtils.h"
+
+#include "hunspell_csutil.hxx"
+
+using namespace mozilla;
+
+mozHunspellFileMgrHost::mozHunspellFileMgrHost(const nsCString& aFilename) {
+  nsCOMPtr<nsIChannel> channel;
+  DebugOnly<Result<Ok, nsresult>> result = Open(aFilename, channel, mStream);
+  NS_WARNING_ASSERTION(result.value.isOk(), "Failed to open Hunspell file");
+}
+
+/* static */
+Result<Ok, nsresult> mozHunspellFileMgrHost::Open(
+    const nsCString& aPath, nsCOMPtr<nsIChannel>& aChannel,
+    nsCOMPtr<nsIInputStream>& aStream) {
+  nsCOMPtr<nsIURI> uri;
+  MOZ_TRY(NS_NewURI(getter_AddRefs(uri), aPath));
+
+  MOZ_TRY(NS_NewChannel(
+      getter_AddRefs(aChannel), uri, nsContentUtils::GetSystemPrincipal(),
+      nsILoadInfo::SEC_REQUIRE_SAME_ORIGIN_INHERITS_SEC_CONTEXT,
+      nsIContentPolicy::TYPE_OTHER));
+
+  MOZ_TRY(aChannel->Open(getter_AddRefs(aStream)));
+  return Ok();
+}
+
+Result<Ok, nsresult> mozHunspellFileMgrHost::ReadLine(nsCString& aLine) {
+  if (!mStream) {
+    return Err(NS_ERROR_NOT_INITIALIZED);
+  }
+
+  bool ok;
+  MOZ_TRY(NS_ReadLine(mStream.get(), &mLineBuffer, aLine, &ok));
+  if (!ok) {
+    mStream = nullptr;
+  }
+
+  mLineNum++;
+  return Ok();
+}
+
+/* static */
+Result<int64_t, nsresult> mozHunspellFileMgrHost::GetSize(
+    const nsCString& aFilename) {
+  int64_t ret = -1;
+
+  nsCOMPtr<nsIChannel> channel;
+  nsCOMPtr<nsIInputStream> stream;
+  MOZ_TRY(Open(aFilename, channel, stream));
+
+  channel->GetContentLength(&ret);
+  return ret;
+}
+
+bool mozHunspellFileMgrHost::GetLine(std::string& aResult) {
+  nsAutoCString line;
+  auto res = ReadLine(line);
+  if (res.isErr()) {
+    return false;
+  }
+
+  aResult.assign(line.BeginReading(), line.Length());
+  return true;
+}
+
+/* static */
+uint32_t mozHunspellCallbacks::sCurrentFreshId = 0;
+/* static */
+mozilla::StaticRWLock mozHunspellCallbacks::sFileMgrMapLock;
+/* static */
+std::map<uint32_t, std::unique_ptr<mozHunspellFileMgrHost>>
+    mozHunspellCallbacks::sFileMgrMap;
+/* static */
+std::set<nsCString> mozHunspellCallbacks::sFileMgrAllowList;
+
+/* static */
+void mozHunspellCallbacks::AllowFile(const nsCString& aFilename) {
+  mozilla::StaticAutoWriteLock lock(sFileMgrMapLock);
+  sFileMgrAllowList.insert(aFilename);
+}
+
+/* static */
+void mozHunspellCallbacks::Clear() {
+  mozilla::StaticAutoWriteLock lock(sFileMgrMapLock);
+  sCurrentFreshId = 0;
+  sFileMgrMap.clear();
+  sFileMgrAllowList.clear();
+}
+
+/* static */
+tainted_hunspell<uint32_t> mozHunspellCallbacks::CreateFilemgr(
+    rlbox_sandbox_hunspell& aSandbox,
+    tainted_hunspell<const char*> t_aFilename) {
+  mozilla::StaticAutoWriteLock lock(sFileMgrMapLock);
+
+  return t_aFilename.copy_and_verify_string(
+      [&](std::unique_ptr<char[]> aFilename) {
+        nsCString cFilename = nsDependentCString(aFilename.get());
+
+        // Ensure that the filename is in the allowlist
+        auto it = sFileMgrAllowList.find(cFilename);
+        MOZ_RELEASE_ASSERT(it != sFileMgrAllowList.end());
+
+        // Get new id
+        uint32_t freshId = GetFreshId();
+        // Save mapping of id to file manager
+        sFileMgrMap[freshId] = std::unique_ptr<mozHunspellFileMgrHost>(
+            new mozHunspellFileMgrHost(cFilename));
+
+        return freshId;
+      });
+}
+
+/* static */
+uint32_t mozHunspellCallbacks::GetFreshId() {
+  // i is uint64_t to prevent overflow during loop increment which would cause
+  // an infinite loop
+  for (uint64_t i = sCurrentFreshId; i < std::numeric_limits<uint32_t>::max();
+       i++) {
+    auto it = sFileMgrMap.find(i);
+    if (it == sFileMgrMap.end()) {
+      // set sCurrentFreshId to the next (possibly) available id
+      sCurrentFreshId = i + 1;
+      return static_cast<uint32_t>(i);
+    }
+  }
+
+  MOZ_CRASH("Ran out of unique file ids for hunspell dictionaries");
+}
+
+/* static */
+mozHunspellFileMgrHost& mozHunspellCallbacks::GetMozHunspellFileMgrHost(
+    tainted_hunspell<uint32_t> t_aFd) {
+  mozilla::StaticAutoReadLock lock(sFileMgrMapLock);
+  uint32_t aFd = t_aFd.copy_and_verify([](uint32_t aFd) { return aFd; });
+  auto iter = sFileMgrMap.find(aFd);
+  MOZ_RELEASE_ASSERT(iter != sFileMgrMap.end());
+  return *(iter->second.get());
+}
+
+/* static */
+tainted_hunspell<bool> mozHunspellCallbacks::GetLine(
+    rlbox_sandbox_hunspell& aSandbox, tainted_hunspell<uint32_t> t_aFd,
+    tainted_hunspell<char**> t_aLinePtr) {
+  mozHunspellFileMgrHost& inst =
+      mozHunspellCallbacks::GetMozHunspellFileMgrHost(t_aFd);
+  std::string line;
+  bool ok = inst.GetLine(line);
+  // If the getline fails, return a null which is "graceful" failure
+  if (ok) {
+    // Copy the line into the sandbox. This memory is eventually freed by
+    // hunspell.
+    size_t size = line.size() + 1;
+    tainted_hunspell<char*> t_line = aSandbox.malloc_in_sandbox<char>(size);
+
+    if (t_line == nullptr) {
+      // If malloc fails, we should go to "graceful" failure path
+      ok = false;
+    } else {
+      rlbox::memcpy(aSandbox, t_line, line.c_str(), size);
+    }
+    *t_aLinePtr = t_line;
+  } else {
+    *t_aLinePtr = nullptr;
+  }
+  return ok;
+}
+
+/* static */
+tainted_hunspell<int> mozHunspellCallbacks::GetLineNum(
+    rlbox_sandbox_hunspell& aSandbox, tainted_hunspell<uint32_t> t_aFd) {
+  mozHunspellFileMgrHost& inst =
+      mozHunspellCallbacks::GetMozHunspellFileMgrHost(t_aFd);
+  int num = inst.GetLineNum();
+  return num;
+}
+
+/* static */
+void mozHunspellCallbacks::DestructFilemgr(rlbox_sandbox_hunspell& aSandbox,
+                                           tainted_hunspell<uint32_t> t_aFd) {
+  mozilla::StaticAutoWriteLock lock(sFileMgrMapLock);
+  uint32_t aFd = t_aFd.copy_and_verify([](uint32_t aFd) { return aFd; });
+
+  auto iter = sFileMgrMap.find(aFd);
+  if (iter != sFileMgrMap.end()) {
+    sFileMgrMap.erase(iter);
+  }
+}
+
+// Callbacks for using Firefox's encoding instead of hunspell's
+
+/* static */
+tainted_hunspell<uint32_t> mozHunspellCallbacks::ToUpperCase(
+    rlbox_sandbox_hunspell& aSandbox, tainted_hunspell<uint32_t> t_aChar) {
+  uint32_t aChar =
+      t_aChar.copy_and_verify([](uint32_t aChar) { return aChar; });
+  return ::ToUpperCase(aChar);
+}
+
+/* static */
+tainted_hunspell<uint32_t> mozHunspellCallbacks::ToLowerCase(
+    rlbox_sandbox_hunspell& aSandbox, tainted_hunspell<uint32_t> t_aChar) {
+  uint32_t aChar =
+      t_aChar.copy_and_verify([](uint32_t aChar) { return aChar; });
+  return ::ToLowerCase(aChar);
+}
+
+/* static */ tainted_hunspell<struct cs_info*>
+mozHunspellCallbacks::GetCurrentCS(rlbox_sandbox_hunspell& aSandbox,
+                                   tainted_hunspell<const char*> t_es) {
+  tainted_hunspell<struct cs_info*> t_ccs =
+      aSandbox.malloc_in_sandbox<struct cs_info>(256);
+  MOZ_RELEASE_ASSERT(t_ccs);
+  return t_es.copy_and_verify_string([&](std::unique_ptr<char[]> es) {
+    struct cs_info* ccs = hunspell_get_current_cs(es.get());
+    rlbox::memcpy(aSandbox, t_ccs, ccs, sizeof(struct cs_info) * 256);
+    delete[] ccs;
+    return t_ccs;
+  });
+}
diff --git a/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxHost.h b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxHost.h
new file mode 100644
index 0000000000..f92070eabf
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxHost.h
@@ -0,0 +1,122 @@
+/* -*- 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 mozHunspellRLBoxHost_h
+#define mozHunspellRLBoxHost_h
+
+#include <map>
+#include <memory>
+#include <mutex>
+#include <set>
+#include <stdint.h>
+#include <string>
+
+#include "RLBoxHunspell.h"
+#include "mozilla/Result.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/RWLock.h"
+#include "nsIChannel.h"
+#include "nsIInputStream.h"
+#include "nsReadLine.h"
+
+namespace mozilla {
+
+class mozHunspellFileMgrHost final {
+ public:
+  /**
+   * aFilename must be a local file/jar URI for the file to load.
+   */
+  explicit mozHunspellFileMgrHost(const nsCString& aFilename);
+  ~mozHunspellFileMgrHost() = default;
+
+  bool GetLine(std::string& aResult);
+  int GetLineNum() const { return mLineNum; }
+
+  static Result<int64_t, nsresult> GetSize(const nsCString& aFilename);
+
+ private:
+  static mozilla::Result<mozilla::Ok, nsresult> Open(
+      const nsCString& aPath, nsCOMPtr<nsIChannel>& aChannel,
+      nsCOMPtr<nsIInputStream>& aStream);
+
+  mozilla::Result<mozilla::Ok, nsresult> ReadLine(nsCString& aLine);
+
+  int mLineNum = 0;
+  nsCOMPtr<nsIInputStream> mStream;
+  nsLineBuffer<char> mLineBuffer;
+};
+
+class mozHunspellCallbacks {
+ public:
+  // APIs invoked by the sandboxed hunspell file manager
+  static tainted_hunspell<uint32_t> CreateFilemgr(
+      rlbox_sandbox_hunspell& aSandbox,
+      tainted_hunspell<const char*> t_aFilename);
+  static tainted_hunspell<bool> GetLine(rlbox_sandbox_hunspell& aSandbox,
+                                        tainted_hunspell<uint32_t> t_aFd,
+                                        tainted_hunspell<char**> t_aLinePtr);
+  static tainted_hunspell<int> GetLineNum(rlbox_sandbox_hunspell& aSandbox,
+                                          tainted_hunspell<uint32_t> t_aFd);
+  static void DestructFilemgr(rlbox_sandbox_hunspell& aSandbox,
+                              tainted_hunspell<uint32_t> t_aFd);
+
+  // APIs necessary for hunspell UTF encoding
+  static tainted_hunspell<uint32_t> ToUpperCase(
+      rlbox_sandbox_hunspell& aSandbox, tainted_hunspell<uint32_t> t_aChar);
+  static tainted_hunspell<uint32_t> ToLowerCase(
+      rlbox_sandbox_hunspell& aSandbox, tainted_hunspell<uint32_t> t_aChar);
+  static tainted_hunspell<struct cs_info*> GetCurrentCS(
+      rlbox_sandbox_hunspell& aSandbox, tainted_hunspell<const char*> t_es);
+
+ protected:
+  // API called by RLBox
+
+  /**
+   * Add filename to allow list.
+   */
+  static void AllowFile(const nsCString& aFilename);
+  friend RLBoxHunspell* RLBoxHunspell::Create(const nsCString& affpath,
+                                              const nsCString& dpath);
+  /**
+   * Clear allow list and map of hunspell file managers.
+   */
+  static void Clear();
+  friend RLBoxHunspell::~RLBoxHunspell();
+
+ private:
+  /**
+   * sFileMgrMap holds a map between unique uint32_t
+   * integers and mozHunspellFileMgrHost instances
+   */
+  static std::map<uint32_t, std::unique_ptr<mozHunspellFileMgrHost>>
+      sFileMgrMap;
+
+  /**
+   * sFileMgrAllowList contains the filenames of the dictionary files hunspell
+   * is allowed to open
+   */
+  static std::set<nsCString> sFileMgrAllowList;
+  /**
+   * Reader-writer lock for the sFileMgrMap
+   */
+  static mozilla::StaticRWLock sFileMgrMapLock;
+  /**
+   * Tracks the next possibly unused id for sFileMgrMap
+   */
+  static uint32_t sCurrentFreshId;
+  /**
+   * Returns an unused id for sFileMgrMap
+   */
+  static uint32_t GetFreshId();
+  /**
+   * Returns the mozHunspellFileMgrHost for the given uint32_t id
+   */
+  static mozHunspellFileMgrHost& GetMozHunspellFileMgrHost(
+      tainted_hunspell<uint32_t> t_aFd);
+};
+}  // namespace mozilla
+
+#endif
diff --git a/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxSandbox.cpp b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxSandbox.cpp
new file mode 100644
index 0000000000..f913b4bc83
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxSandbox.cpp
@@ -0,0 +1,54 @@
+/* -*- 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 "mozHunspellRLBoxSandbox.h"
+#include "mozHunspellRLBoxGlue.h"
+
+FileMgr::FileMgr(const char* aFilename, const char* aKey) : mFd(0) {
+  // The key is not used in firefox
+  mFd = moz_glue_hunspell_create_filemgr(aFilename);
+}
+
+bool FileMgr::getline(std::string& aResult) {
+  char* line = nullptr;
+  bool ok = moz_glue_hunspell_get_line(mFd, &line);
+  if (ok && line) {
+    aResult = line;
+    free(line);
+  }
+  return ok;
+}
+
+int FileMgr::getlinenum() const { return moz_glue_hunspell_get_line_num(mFd); }
+
+FileMgr::~FileMgr() { moz_glue_hunspell_destruct_filemgr(mFd); }
+
+// Glue code to set global callbacks
+
+hunspell_create_filemgr_t* moz_glue_hunspell_create_filemgr = nullptr;
+hunspell_get_line_t* moz_glue_hunspell_get_line = nullptr;
+hunspell_get_line_num_t* moz_glue_hunspell_get_line_num = nullptr;
+hunspell_destruct_filemgr_t* moz_glue_hunspell_destruct_filemgr = nullptr;
+hunspell_ToUpperCase_t* moz_hunspell_ToUpperCase = nullptr;
+hunspell_ToLowerCase_t* moz_hunspell_ToLowerCase = nullptr;
+hunspell_get_current_cs_t* moz_hunspell_GetCurrentCS = nullptr;
+
+void RegisterHunspellCallbacks(
+    hunspell_create_filemgr_t* aHunspellCreateFilemgr,
+    hunspell_get_line_t* aHunspellGetLine,
+    hunspell_get_line_num_t* aHunspellGetLine_num,
+    hunspell_destruct_filemgr_t* aHunspellDestructFilemgr,
+    hunspell_ToUpperCase_t* aHunspellToUpperCase,
+    hunspell_ToLowerCase_t* aHunspellToLowerCase,
+    hunspell_get_current_cs_t* aHunspellGetCurrentCS) {
+  moz_glue_hunspell_create_filemgr = aHunspellCreateFilemgr;
+  moz_glue_hunspell_get_line = aHunspellGetLine;
+  moz_glue_hunspell_get_line_num = aHunspellGetLine_num;
+  moz_glue_hunspell_destruct_filemgr = aHunspellDestructFilemgr;
+  moz_hunspell_ToUpperCase = aHunspellToUpperCase;
+  moz_hunspell_ToLowerCase = aHunspellToLowerCase;
+  moz_hunspell_GetCurrentCS = aHunspellGetCurrentCS;
+}
diff --git a/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxSandbox.h b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxSandbox.h
new file mode 100644
index 0000000000..9850408807
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspellRLBoxSandbox.h
@@ -0,0 +1,36 @@
+/* -*- 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 mozHunspellRLBoxSandbox_h
+#define mozHunspellRLBoxSandbox_h
+
+#include <string>
+#include <stdint.h>
+
+// Note: This class name and lack of namespacing terrible, but are necessary
+// for Hunspell compatibility.
+class FileMgr final {
+ public:
+  /**
+   * aFilename must be a local file/jar URI for the file to load.
+   *
+   * aKey is the decription key for encrypted Hunzip files, and is
+   * unsupported. The argument is there solely for compatibility.
+   */
+  explicit FileMgr(const char* aFilename, const char* aKey = nullptr);
+  ~FileMgr();
+
+  // Note: The nonstandard naming conventions of these methods are necessary for
+  // Hunspell compatibility.
+  bool getline(std::string& aLine);
+  int getlinenum() const;
+
+ private:
+  // opaque file descriptor got from the host application
+  uint32_t mFd;
+};
+
+#endif  // mozHunspellRLBoxSandbox_h