Adding upstream version 124.0.1.upstream/124.0.1

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

59 files changed, 8521 insertions, 0 deletions

diff --git a/editor/spellchecker/EditorSpellCheck.cpp b/editor/spellchecker/EditorSpellCheck.cpp
new file mode 100644
index 0000000000..cc5fcab9aa
--- /dev/null
+++ b/editor/spellchecker/EditorSpellCheck.cpp
@@ -0,0 +1,1183 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 sts=2 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 "EditorSpellCheck.h"
+
+#include "EditorBase.h"            // for EditorBase
+#include "HTMLEditor.h"            // for HTMLEditor
+#include "TextServicesDocument.h"  // for TextServicesDocument
+
+#include "mozilla/Attributes.h"   // for final
+#include "mozilla/dom/Element.h"  // for Element
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/Selection.h"
+#include "mozilla/dom/StaticRange.h"
+#include "mozilla/intl/Locale.h"         // for mozilla::intl::Locale
+#include "mozilla/intl/LocaleService.h"  // for retrieving app locale
+#include "mozilla/intl/OSPreferences.h"  // for mozilla::intl::OSPreferences
+#include "mozilla/Logging.h"             // for mozilla::LazyLogModule
+#include "mozilla/mozalloc.h"            // for operator delete, etc
+#include "mozilla/mozSpellChecker.h"     // for mozSpellChecker
+#include "mozilla/Preferences.h"         // for Preferences
+
+#include "nsAString.h"                // for nsAString::IsEmpty, etc
+#include "nsComponentManagerUtils.h"  // for do_CreateInstance
+#include "nsDebug.h"                  // for NS_ENSURE_TRUE, etc
+#include "nsDependentSubstring.h"     // for Substring
+#include "nsError.h"                  // for NS_ERROR_NOT_INITIALIZED, etc
+#include "nsIContent.h"               // for nsIContent
+#include "nsIContentPrefService2.h"   // for nsIContentPrefService2, etc
+#include "mozilla/dom/Document.h"     // for Document
+#include "nsIEditor.h"                // for nsIEditor
+#include "nsILoadContext.h"
+#include "nsISupports.h"       // for nsISupports
+#include "nsISupportsUtils.h"  // for NS_ADDREF
+#include "nsIURI.h"            // for nsIURI
+#include "nsThreadUtils.h"     // for GetMainThreadSerialEventTarget
+#include "nsVariant.h"         // for nsIWritableVariant, etc
+#include "nsLiteralString.h"   // for NS_LITERAL_STRING, etc
+#include "nsRange.h"
+#include "nsReadableUtils.h"        // for ToNewUnicode, EmptyString, etc
+#include "nsServiceManagerUtils.h"  // for do_GetService
+#include "nsString.h"               // for nsAutoString, nsString, etc
+#include "nsStringFwd.h"            // for nsAFlatString
+#include "nsStyleUtil.h"            // for nsStyleUtil
+#include "nsXULAppAPI.h"            // for XRE_GetProcessType
+
+namespace mozilla {
+
+using namespace dom;
+using intl::LocaleService;
+using intl::OSPreferences;
+
+static mozilla::LazyLogModule sEditorSpellChecker("EditorSpellChecker");
+
+class UpdateDictionaryHolder {
+ private:
+  EditorSpellCheck* mSpellCheck;
+
+ public:
+  explicit UpdateDictionaryHolder(EditorSpellCheck* esc) : mSpellCheck(esc) {
+    if (mSpellCheck) {
+      mSpellCheck->BeginUpdateDictionary();
+    }
+  }
+
+  ~UpdateDictionaryHolder() {
+    if (mSpellCheck) {
+      mSpellCheck->EndUpdateDictionary();
+    }
+  }
+};
+
+#define CPS_PREF_NAME u"spellcheck.lang"_ns
+
+/**
+ * Gets the URI of aEditor's document.
+ */
+static nsIURI* GetDocumentURI(EditorBase* aEditor) {
+  MOZ_ASSERT(aEditor);
+
+  Document* doc = aEditor->AsEditorBase()->GetDocument();
+  if (NS_WARN_IF(!doc)) {
+    return nullptr;
+  }
+
+  return doc->GetDocumentURI();
+}
+
+static nsILoadContext* GetLoadContext(nsIEditor* aEditor) {
+  Document* doc = aEditor->AsEditorBase()->GetDocument();
+  if (NS_WARN_IF(!doc)) {
+    return nullptr;
+  }
+
+  return doc->GetLoadContext();
+}
+
+static nsCString DictionariesToString(
+    const nsTArray<nsCString>& aDictionaries) {
+  nsCString asString;
+  for (const auto& dictionary : aDictionaries) {
+    asString.Append(dictionary);
+    asString.Append(',');
+  }
+  return asString;
+}
+
+static void StringToDictionaries(const nsCString& aString,
+                                 nsTArray<nsCString>& aDictionaries) {
+  nsTArray<nsCString> asDictionaries;
+  for (const nsACString& token :
+       nsCCharSeparatedTokenizer(aString, ',').ToRange()) {
+    if (token.IsEmpty()) {
+      continue;
+    }
+    aDictionaries.AppendElement(token);
+  }
+}
+
+/**
+ * Fetches the dictionary stored in content prefs and maintains state during the
+ * fetch, which is asynchronous.
+ */
+class DictionaryFetcher final : public nsIContentPrefCallback2 {
+ public:
+  NS_DECL_ISUPPORTS
+
+  DictionaryFetcher(EditorSpellCheck* aSpellCheck,
+                    nsIEditorSpellCheckCallback* aCallback, uint32_t aGroup)
+      : mCallback(aCallback), mGroup(aGroup), mSpellCheck(aSpellCheck) {}
+
+  NS_IMETHOD Fetch(nsIEditor* aEditor);
+
+  NS_IMETHOD HandleResult(nsIContentPref* aPref) override {
+    nsCOMPtr<nsIVariant> value;
+    nsresult rv = aPref->GetValue(getter_AddRefs(value));
+    NS_ENSURE_SUCCESS(rv, rv);
+    nsCString asString;
+    value->GetAsACString(asString);
+    StringToDictionaries(asString, mDictionaries);
+    return NS_OK;
+  }
+
+  NS_IMETHOD HandleCompletion(uint16_t reason) override {
+    mSpellCheck->DictionaryFetched(this);
+    return NS_OK;
+  }
+
+  NS_IMETHOD HandleError(nsresult error) override { return NS_OK; }
+
+  nsCOMPtr<nsIEditorSpellCheckCallback> mCallback;
+  uint32_t mGroup;
+  RefPtr<nsAtom> mRootContentLang;
+  RefPtr<nsAtom> mRootDocContentLang;
+  nsTArray<nsCString> mDictionaries;
+
+ private:
+  ~DictionaryFetcher() {}
+
+  RefPtr<EditorSpellCheck> mSpellCheck;
+};
+
+NS_IMPL_ISUPPORTS(DictionaryFetcher, nsIContentPrefCallback2)
+
+class ContentPrefInitializerRunnable final : public Runnable {
+ public:
+  ContentPrefInitializerRunnable(nsIEditor* aEditor,
+                                 nsIContentPrefCallback2* aCallback)
+      : Runnable("ContentPrefInitializerRunnable"),
+        mEditorBase(aEditor->AsEditorBase()),
+        mCallback(aCallback) {}
+
+  NS_IMETHOD Run() override {
+    if (mEditorBase->Destroyed()) {
+      mCallback->HandleError(NS_ERROR_NOT_AVAILABLE);
+      return NS_OK;
+    }
+
+    nsCOMPtr<nsIContentPrefService2> contentPrefService =
+        do_GetService(NS_CONTENT_PREF_SERVICE_CONTRACTID);
+    if (NS_WARN_IF(!contentPrefService)) {
+      mCallback->HandleError(NS_ERROR_NOT_AVAILABLE);
+      return NS_OK;
+    }
+
+    nsCOMPtr<nsIURI> docUri = GetDocumentURI(mEditorBase);
+    if (NS_WARN_IF(!docUri)) {
+      mCallback->HandleError(NS_ERROR_FAILURE);
+      return NS_OK;
+    }
+
+    nsAutoCString docUriSpec;
+    nsresult rv = docUri->GetSpec(docUriSpec);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mCallback->HandleError(rv);
+      return NS_OK;
+    }
+
+    rv = contentPrefService->GetByDomainAndName(
+        NS_ConvertUTF8toUTF16(docUriSpec), CPS_PREF_NAME,
+        GetLoadContext(mEditorBase), mCallback);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mCallback->HandleError(rv);
+      return NS_OK;
+    }
+    return NS_OK;
+  }
+
+ private:
+  RefPtr<EditorBase> mEditorBase;
+  nsCOMPtr<nsIContentPrefCallback2> mCallback;
+};
+
+NS_IMETHODIMP
+DictionaryFetcher::Fetch(nsIEditor* aEditor) {
+  NS_ENSURE_ARG_POINTER(aEditor);
+
+  nsCOMPtr<nsIRunnable> runnable =
+      new ContentPrefInitializerRunnable(aEditor, this);
+  NS_DispatchToCurrentThreadQueue(runnable.forget(), 1000,
+                                  EventQueuePriority::Idle);
+
+  return NS_OK;
+}
+
+/**
+ * Stores the current dictionary for aEditor's document URL.
+ */
+static nsresult StoreCurrentDictionaries(
+    EditorBase* aEditorBase, const nsTArray<nsCString>& aDictionaries) {
+  NS_ENSURE_ARG_POINTER(aEditorBase);
+
+  nsresult rv;
+
+  nsCOMPtr<nsIURI> docUri = GetDocumentURI(aEditorBase);
+  if (NS_WARN_IF(!docUri)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoCString docUriSpec;
+  rv = docUri->GetSpec(docUriSpec);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  RefPtr<nsVariant> prefValue = new nsVariant();
+
+  nsCString asString = DictionariesToString(aDictionaries);
+  prefValue->SetAsAString(NS_ConvertUTF8toUTF16(asString));
+
+  nsCOMPtr<nsIContentPrefService2> contentPrefService =
+      do_GetService(NS_CONTENT_PREF_SERVICE_CONTRACTID);
+  NS_ENSURE_TRUE(contentPrefService, NS_ERROR_NOT_INITIALIZED);
+
+  return contentPrefService->Set(NS_ConvertUTF8toUTF16(docUriSpec),
+                                 CPS_PREF_NAME, prefValue,
+                                 GetLoadContext(aEditorBase), nullptr);
+}
+
+/**
+ * Forgets the current dictionary stored for aEditor's document URL.
+ */
+static nsresult ClearCurrentDictionaries(EditorBase* aEditorBase) {
+  NS_ENSURE_ARG_POINTER(aEditorBase);
+
+  nsresult rv;
+
+  nsCOMPtr<nsIURI> docUri = GetDocumentURI(aEditorBase);
+  if (NS_WARN_IF(!docUri)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoCString docUriSpec;
+  rv = docUri->GetSpec(docUriSpec);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIContentPrefService2> contentPrefService =
+      do_GetService(NS_CONTENT_PREF_SERVICE_CONTRACTID);
+  NS_ENSURE_TRUE(contentPrefService, NS_ERROR_NOT_INITIALIZED);
+
+  return contentPrefService->RemoveByDomainAndName(
+      NS_ConvertUTF8toUTF16(docUriSpec), CPS_PREF_NAME,
+      GetLoadContext(aEditorBase), nullptr);
+}
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(EditorSpellCheck)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(EditorSpellCheck)
+
+NS_INTERFACE_MAP_BEGIN(EditorSpellCheck)
+  NS_INTERFACE_MAP_ENTRY(nsIEditorSpellCheck)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIEditorSpellCheck)
+  NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(EditorSpellCheck)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION(EditorSpellCheck, mEditor, mSpellChecker)
+
+EditorSpellCheck::EditorSpellCheck()
+    : mTxtSrvFilterType(0),
+      mSuggestedWordIndex(0),
+      mDictionaryIndex(0),
+      mDictionaryFetcherGroup(0),
+      mUpdateDictionaryRunning(false) {}
+
+EditorSpellCheck::~EditorSpellCheck() {
+  // Make sure we blow the spellchecker away, just in
+  // case it hasn't been destroyed already.
+  mSpellChecker = nullptr;
+}
+
+mozSpellChecker* EditorSpellCheck::GetSpellChecker() { return mSpellChecker; }
+
+// The problem is that if the spell checker does not exist, we can not tell
+// which dictionaries are installed. This function works around the problem,
+// allowing callers to ask if we can spell check without actually doing so (and
+// enabling or disabling UI as necessary). This just creates a spellcheck
+// object if needed and asks it for the dictionary list.
+NS_IMETHODIMP
+EditorSpellCheck::CanSpellCheck(bool* aCanSpellCheck) {
+  RefPtr<mozSpellChecker> spellChecker = mSpellChecker;
+  if (!spellChecker) {
+    spellChecker = mozSpellChecker::Create();
+    MOZ_ASSERT(spellChecker);
+  }
+  nsTArray<nsCString> dictList;
+  nsresult rv = spellChecker->GetDictionaryList(&dictList);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  *aCanSpellCheck = !dictList.IsEmpty();
+  return NS_OK;
+}
+
+// Instances of this class can be used as either runnables or RAII helpers.
+class CallbackCaller final : public Runnable {
+ public:
+  explicit CallbackCaller(nsIEditorSpellCheckCallback* aCallback)
+      : mozilla::Runnable("CallbackCaller"), mCallback(aCallback) {}
+
+  ~CallbackCaller() { Run(); }
+
+  NS_IMETHOD Run() override {
+    if (mCallback) {
+      mCallback->EditorSpellCheckDone();
+      mCallback = nullptr;
+    }
+    return NS_OK;
+  }
+
+ private:
+  nsCOMPtr<nsIEditorSpellCheckCallback> mCallback;
+};
+
+NS_IMETHODIMP
+EditorSpellCheck::InitSpellChecker(nsIEditor* aEditor,
+                                   bool aEnableSelectionChecking,
+                                   nsIEditorSpellCheckCallback* aCallback) {
+  NS_ENSURE_TRUE(aEditor, NS_ERROR_NULL_POINTER);
+  mEditor = aEditor->AsEditorBase();
+
+  RefPtr<Document> doc = mEditor->GetDocument();
+  if (NS_WARN_IF(!doc)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsresult rv;
+
+  // We can spell check with any editor type
+  RefPtr<TextServicesDocument> textServicesDocument =
+      new TextServicesDocument();
+  textServicesDocument->SetFilterType(mTxtSrvFilterType);
+
+  // EditorBase::AddEditActionListener() needs to access mSpellChecker and
+  // mSpellChecker->GetTextServicesDocument().  Therefore, we need to
+  // initialize them before calling TextServicesDocument::InitWithEditor()
+  // since it calls EditorBase::AddEditActionListener().
+  mSpellChecker = mozSpellChecker::Create();
+  MOZ_ASSERT(mSpellChecker);
+  rv = mSpellChecker->SetDocument(textServicesDocument, true);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Pass the editor to the text services document
+  rv = textServicesDocument->InitWithEditor(aEditor);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (aEnableSelectionChecking) {
+    // Find out if the section is collapsed or not.
+    // If it isn't, we want to spellcheck just the selection.
+
+    RefPtr<Selection> selection;
+    aEditor->GetSelection(getter_AddRefs(selection));
+    if (NS_WARN_IF(!selection)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    if (selection->RangeCount()) {
+      RefPtr<const nsRange> range = selection->GetRangeAt(0);
+      NS_ENSURE_STATE(range);
+
+      if (!range->Collapsed()) {
+        // We don't want to touch the range in the selection,
+        // so create a new copy of it.
+        RefPtr<StaticRange> staticRange =
+            StaticRange::Create(range, IgnoreErrors());
+        if (NS_WARN_IF(!staticRange)) {
+          return NS_ERROR_FAILURE;
+        }
+
+        // Make sure the new range spans complete words.
+        rv = textServicesDocument->ExpandRangeToWordBoundaries(staticRange);
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return rv;
+        }
+
+        // Now tell the text services that you only want
+        // to iterate over the text in this range.
+        rv = textServicesDocument->SetExtent(staticRange);
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return rv;
+        }
+      }
+    }
+  }
+  // do not fail if UpdateCurrentDictionary fails because this method may
+  // succeed later.
+  rv = UpdateCurrentDictionary(aCallback);
+  if (NS_FAILED(rv) && aCallback) {
+    // However, if it does fail, we still need to call the callback since we
+    // discard the failure.  Do it asynchronously so that the caller is always
+    // guaranteed async behavior.
+    RefPtr<CallbackCaller> caller = new CallbackCaller(aCallback);
+    rv = doc->Dispatch(caller.forget());
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::GetNextMisspelledWord(nsAString& aNextMisspelledWord) {
+  MOZ_LOG(sEditorSpellChecker, LogLevel::Debug, ("%s", __FUNCTION__));
+
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  DeleteSuggestedWordList();
+  // Beware! This may flush notifications via synchronous
+  // ScrollSelectionIntoView.
+  RefPtr<mozSpellChecker> spellChecker(mSpellChecker);
+  return spellChecker->NextMisspelledWord(aNextMisspelledWord,
+                                          mSuggestedWordList);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::GetSuggestedWord(nsAString& aSuggestedWord) {
+  // XXX This is buggy if mSuggestedWordList.Length() is over INT32_MAX.
+  if (mSuggestedWordIndex < static_cast<int32_t>(mSuggestedWordList.Length())) {
+    aSuggestedWord = mSuggestedWordList[mSuggestedWordIndex];
+    mSuggestedWordIndex++;
+  } else {
+    // A blank string signals that there are no more strings
+    aSuggestedWord.Truncate();
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::CheckCurrentWord(const nsAString& aSuggestedWord,
+                                   bool* aIsMisspelled) {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  DeleteSuggestedWordList();
+  return mSpellChecker->CheckWord(aSuggestedWord, aIsMisspelled,
+                                  &mSuggestedWordList);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::Suggest(const nsAString& aSuggestedWord, uint32_t aCount,
+                          JSContext* aCx, Promise** aPromise) {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  nsIGlobalObject* globalObject = xpc::CurrentNativeGlobal(aCx);
+  if (NS_WARN_IF(!globalObject)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  ErrorResult result;
+  RefPtr<Promise> promise = Promise::Create(globalObject, result);
+  if (NS_WARN_IF(result.Failed())) {
+    return result.StealNSResult();
+  }
+
+  mSpellChecker->Suggest(aSuggestedWord, aCount)
+      ->Then(
+          GetMainThreadSerialEventTarget(), __func__,
+          [promise](const CopyableTArray<nsString>& aSuggestions) {
+            promise->MaybeResolve(aSuggestions);
+          },
+          [promise](nsresult aError) {
+            promise->MaybeReject(NS_ERROR_FAILURE);
+          });
+
+  promise.forget(aPromise);
+  return NS_OK;
+}
+
+RefPtr<CheckWordPromise> EditorSpellCheck::CheckCurrentWordsNoSuggest(
+    const nsTArray<nsString>& aSuggestedWords) {
+  if (NS_WARN_IF(!mSpellChecker)) {
+    return CheckWordPromise::CreateAndReject(NS_ERROR_NOT_INITIALIZED,
+                                             __func__);
+  }
+
+  return mSpellChecker->CheckWords(aSuggestedWords);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::ReplaceWord(const nsAString& aMisspelledWord,
+                              const nsAString& aReplaceWord,
+                              bool aAllOccurrences) {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  RefPtr<mozSpellChecker> spellChecker(mSpellChecker);
+  return spellChecker->Replace(aMisspelledWord, aReplaceWord, aAllOccurrences);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::IgnoreWordAllOccurrences(const nsAString& aWord) {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  return mSpellChecker->IgnoreAll(aWord);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::GetPersonalDictionary() {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  // We can spell check with any editor type
+  mDictionaryList.Clear();
+  mDictionaryIndex = 0;
+  return mSpellChecker->GetPersonalDictionary(&mDictionaryList);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::GetPersonalDictionaryWord(nsAString& aDictionaryWord) {
+  // XXX This is buggy if mDictionaryList.Length() is over INT32_MAX.
+  if (mDictionaryIndex < static_cast<int32_t>(mDictionaryList.Length())) {
+    aDictionaryWord = mDictionaryList[mDictionaryIndex];
+    mDictionaryIndex++;
+  } else {
+    // A blank string signals that there are no more strings
+    aDictionaryWord.Truncate();
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::AddWordToDictionary(const nsAString& aWord) {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  return mSpellChecker->AddWordToPersonalDictionary(aWord);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::RemoveWordFromDictionary(const nsAString& aWord) {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  return mSpellChecker->RemoveWordFromPersonalDictionary(aWord);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::GetDictionaryList(nsTArray<nsCString>& aList) {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  return mSpellChecker->GetDictionaryList(&aList);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::GetCurrentDictionaries(nsTArray<nsCString>& aDictionaries) {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+  return mSpellChecker->GetCurrentDictionaries(aDictionaries);
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::SetCurrentDictionaries(
+    const nsTArray<nsCString>& aDictionaries, JSContext* aCx,
+    Promise** aPromise) {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  RefPtr<EditorSpellCheck> kungFuDeathGrip = this;
+
+  // The purpose of mUpdateDictionaryRunning is to avoid doing all of this if
+  // UpdateCurrentDictionary's helper method DictionaryFetched, which calls us,
+  // is on the stack. In other words: Only do this, if the user manually
+  // selected a dictionary to use.
+  if (!mUpdateDictionaryRunning) {
+    // Ignore pending dictionary fetchers by increasing this number.
+    mDictionaryFetcherGroup++;
+
+    uint32_t flags = 0;
+    mEditor->GetFlags(&flags);
+    if (!(flags & nsIEditor::eEditorMailMask)) {
+      bool contentPrefMatchesUserPref = true;
+      // Check if aDictionaries has the same languages as mPreferredLangs.
+      if (!aDictionaries.IsEmpty()) {
+        if (aDictionaries.Length() != mPreferredLangs.Length()) {
+          contentPrefMatchesUserPref = false;
+        } else {
+          for (const auto& dictName : aDictionaries) {
+            if (mPreferredLangs.IndexOf(dictName) ==
+                nsTArray<nsCString>::NoIndex) {
+              contentPrefMatchesUserPref = false;
+              break;
+            }
+          }
+        }
+      }
+      if (!contentPrefMatchesUserPref) {
+        // When user sets dictionary manually, we store this value associated
+        // with editor url, if it doesn't match the document language exactly.
+        // For example on "en" sites, we need to store "en-GB", otherwise
+        // the language might jump back to en-US although the user explicitly
+        // chose otherwise.
+        StoreCurrentDictionaries(mEditor, aDictionaries);
+#ifdef DEBUG_DICT
+        printf("***** Writing content preferences for |%s|\n",
+               DictionariesToString(aDictionaries).Data());
+#endif
+      } else {
+        // If user sets a dictionary matching the language defined by
+        // document, we consider content pref has been canceled, and we clear
+        // it.
+        ClearCurrentDictionaries(mEditor);
+#ifdef DEBUG_DICT
+        printf("***** Clearing content preferences for |%s|\n",
+               DictionariesToString(aDictionaries).Data());
+#endif
+      }
+
+      // Also store it in as a preference, so we can use it as a fallback.
+      // We don't want this for mail composer because it uses
+      // "spellchecker.dictionary" as a preference.
+      //
+      // XXX: Prefs can only be set in the parent process, so this condition is
+      // necessary to stop libpref from throwing errors. But this should
+      // probably be handled in a better way.
+      if (XRE_IsParentProcess()) {
+        nsCString asString = DictionariesToString(aDictionaries);
+        Preferences::SetCString("spellchecker.dictionary", asString);
+#ifdef DEBUG_DICT
+        printf("***** Possibly storing spellchecker.dictionary |%s|\n",
+               asString.Data());
+#endif
+      }
+    } else {
+      MOZ_ASSERT(flags & nsIEditor::eEditorMailMask);
+      // Since the mail editor can only influence the language selection by the
+      // html lang attribute, set the content-language document to persist
+      // multi language selections.
+      // XXX Why doesn't here use the document of the editor directly?
+      nsCOMPtr<nsIContent> anonymousDivOrEditingHost;
+      if (HTMLEditor* htmlEditor = mEditor->GetAsHTMLEditor()) {
+        anonymousDivOrEditingHost = htmlEditor->ComputeEditingHost();
+      } else {
+        anonymousDivOrEditingHost = mEditor->GetRoot();
+      }
+      RefPtr<Document> ownerDoc = anonymousDivOrEditingHost->OwnerDoc();
+      Document* parentDoc = ownerDoc->GetInProcessParentDocument();
+      if (parentDoc) {
+        parentDoc->SetHeaderData(
+            nsGkAtoms::headerContentLanguage,
+            NS_ConvertUTF8toUTF16(DictionariesToString(aDictionaries)));
+      }
+    }
+  }
+
+  nsIGlobalObject* globalObject = xpc::CurrentNativeGlobal(aCx);
+  if (NS_WARN_IF(!globalObject)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  ErrorResult result;
+  RefPtr<Promise> promise = Promise::Create(globalObject, result);
+  if (NS_WARN_IF(result.Failed())) {
+    return result.StealNSResult();
+  }
+
+  mSpellChecker->SetCurrentDictionaries(aDictionaries)
+      ->Then(
+          GetMainThreadSerialEventTarget(), __func__,
+          [promise]() { promise->MaybeResolveWithUndefined(); },
+          [promise](nsresult aError) {
+            promise->MaybeReject(NS_ERROR_FAILURE);
+          });
+
+  promise.forget(aPromise);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::UninitSpellChecker() {
+  NS_ENSURE_TRUE(mSpellChecker, NS_ERROR_NOT_INITIALIZED);
+
+  // Cleanup - kill the spell checker
+  DeleteSuggestedWordList();
+  mDictionaryList.Clear();
+  mDictionaryIndex = 0;
+  mDictionaryFetcherGroup++;
+  mSpellChecker = nullptr;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::SetFilterType(uint32_t aFilterType) {
+  mTxtSrvFilterType = aFilterType;
+  return NS_OK;
+}
+
+nsresult EditorSpellCheck::DeleteSuggestedWordList() {
+  mSuggestedWordList.Clear();
+  mSuggestedWordIndex = 0;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+EditorSpellCheck::UpdateCurrentDictionary(
+    nsIEditorSpellCheckCallback* aCallback) {
+  if (NS_WARN_IF(!mSpellChecker)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  nsresult rv;
+
+  RefPtr<EditorSpellCheck> kungFuDeathGrip = this;
+
+  // Get language with html5 algorithm
+  const RefPtr<Element> rootEditableElement =
+      [](const EditorBase& aEditorBase) -> Element* {
+    if (!aEditorBase.IsHTMLEditor()) {
+      return aEditorBase.GetRoot();
+    }
+    if (aEditorBase.IsMailEditor()) {
+      // Shouldn't run spellcheck in a mail editor without focus
+      // (bug 1507543)
+      // XXX Why doesn't here use the document of the editor directly?
+      Element* const editingHost =
+          aEditorBase.AsHTMLEditor()->ComputeEditingHost();
+      if (!editingHost) {
+        return nullptr;
+      }
+      // Try to get topmost document's document element for embedded mail
+      // editor (bug 967494)
+      Document* parentDoc =
+          editingHost->OwnerDoc()->GetInProcessParentDocument();
+      if (!parentDoc) {
+        return editingHost;
+      }
+      return parentDoc->GetDocumentElement();
+    }
+    return aEditorBase.AsHTMLEditor()->GetFocusedElement();
+  }(*mEditor);
+
+  if (!rootEditableElement) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<DictionaryFetcher> fetcher =
+      new DictionaryFetcher(this, aCallback, mDictionaryFetcherGroup);
+  fetcher->mRootContentLang = rootEditableElement->GetLang();
+  RefPtr<Document> doc = rootEditableElement->GetComposedDoc();
+  NS_ENSURE_STATE(doc);
+  fetcher->mRootDocContentLang = doc->GetContentLanguage();
+
+  rv = fetcher->Fetch(mEditor);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+// Helper function that iterates over the list of dictionaries and sets the one
+// that matches based on a given comparison type.
+bool EditorSpellCheck::BuildDictionaryList(const nsACString& aDictName,
+                                           const nsTArray<nsCString>& aDictList,
+                                           enum dictCompare aCompareType,
+                                           nsTArray<nsCString>& aOutList) {
+  for (const auto& dictStr : aDictList) {
+    bool equals = false;
+    switch (aCompareType) {
+      case DICT_NORMAL_COMPARE:
+        equals = aDictName.Equals(dictStr);
+        break;
+      case DICT_COMPARE_CASE_INSENSITIVE:
+        equals = aDictName.Equals(dictStr, nsCaseInsensitiveCStringComparator);
+        break;
+      case DICT_COMPARE_DASHMATCH:
+        equals = nsStyleUtil::DashMatchCompare(
+            NS_ConvertUTF8toUTF16(dictStr), NS_ConvertUTF8toUTF16(aDictName),
+            nsCaseInsensitiveStringComparator);
+        break;
+    }
+    if (equals) {
+      // Avoid adding duplicates to aOutList.
+      if (aOutList.IndexOf(dictStr) == nsTArray<nsCString>::NoIndex) {
+        aOutList.AppendElement(dictStr);
+      }
+#ifdef DEBUG_DICT
+      printf("***** Trying |%s|.\n", dictStr.get());
+#endif
+      // We always break here. We tried to set the dictionary to an existing
+      // dictionary from the list. This must work, if it doesn't, there is
+      // no point trying another one.
+      return true;
+    }
+  }
+  return false;
+}
+
+nsresult EditorSpellCheck::DictionaryFetched(DictionaryFetcher* aFetcher) {
+  MOZ_ASSERT(aFetcher);
+  RefPtr<EditorSpellCheck> kungFuDeathGrip = this;
+
+  BeginUpdateDictionary();
+
+  if (aFetcher->mGroup < mDictionaryFetcherGroup) {
+    // SetCurrentDictionary was called after the fetch started.  Don't overwrite
+    // that dictionary with the fetched one.
+    EndUpdateDictionary();
+    if (aFetcher->mCallback) {
+      aFetcher->mCallback->EditorSpellCheckDone();
+    }
+    return NS_OK;
+  }
+
+  /*
+   * We try to derive the dictionary to use based on the following priorities:
+   * 1) Content preference, so the language the user set for the site before.
+   *    (Introduced in bug 678842 and corrected in bug 717433.)
+   * 2) Language set by the website, or any other dictionary that partly
+   *    matches that. (Introduced in bug 338427.)
+   *    Eg. if the website is "en-GB", a user who only has "en-US" will get
+   *    that. If the website is generic "en", the user will get one of the
+   *    "en-*" installed. If application locale or system locale is "en-*",
+   *    we get it. If others, it is (almost) random.
+   *    However, we prefer what is stored in "spellchecker.dictionary",
+   *    so if the user chose "en-AU" before, they will get "en-AU" on a plain
+   *    "en" site. (Introduced in bug 682564.)
+   *    If the site has multiple languages declared in its Content-Language
+   *    header and there is no more specific lang tag in HTML, we try to
+   *    enable a dictionary for every content language.
+   * 3) The value of "spellchecker.dictionary" which reflects a previous
+   *    language choice of the user (on another site).
+   *    (This was the original behaviour before the aforementioned bugs
+   *    landed).
+   * 4) The user's locale.
+   * 5) Use the current dictionary that is currently set.
+   * 6) The content of the "LANG" environment variable (if set).
+   * 7) The first spell check dictionary installed.
+   */
+
+  // Get the language from the element or its closest parent according to:
+  // https://html.spec.whatwg.org/#attr-lang
+  // This is used in SetCurrentDictionaries.
+  nsCString contentLangs;
+  // Reset mPreferredLangs so we only get the current state.
+  mPreferredLangs.Clear();
+  if (aFetcher->mRootContentLang) {
+    aFetcher->mRootContentLang->ToUTF8String(contentLangs);
+  }
+#ifdef DEBUG_DICT
+  printf("***** mPreferredLangs (element) |%s|\n", contentLangs.get());
+#endif
+  if (!contentLangs.IsEmpty()) {
+    mPreferredLangs.AppendElement(contentLangs);
+  } else {
+    // If no luck, try the "Content-Language" header.
+    if (aFetcher->mRootDocContentLang) {
+      aFetcher->mRootDocContentLang->ToUTF8String(contentLangs);
+    }
+#ifdef DEBUG_DICT
+    printf("***** mPreferredLangs (content-language) |%s|\n",
+           contentLangs.get());
+#endif
+    StringToDictionaries(contentLangs, mPreferredLangs);
+  }
+
+  // We obtain a list of available dictionaries.
+  AutoTArray<nsCString, 8> dictList;
+  nsresult rv = mSpellChecker->GetDictionaryList(&dictList);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    EndUpdateDictionary();
+    if (aFetcher->mCallback) {
+      aFetcher->mCallback->EditorSpellCheckDone();
+    }
+    return rv;
+  }
+
+  // Priority 1:
+  // If we successfully fetched a dictionary from content prefs, do not go
+  // further. Use this exact dictionary.
+  // Don't use content preferences for editor with eEditorMailMask flag.
+  nsAutoCString dictName;
+  uint32_t flags;
+  mEditor->GetFlags(&flags);
+  if (!(flags & nsIEditor::eEditorMailMask)) {
+    if (!aFetcher->mDictionaries.IsEmpty()) {
+      RefPtr<EditorSpellCheck> self = this;
+      RefPtr<DictionaryFetcher> fetcher = aFetcher;
+      mSpellChecker->SetCurrentDictionaries(aFetcher->mDictionaries)
+          ->Then(
+              GetMainThreadSerialEventTarget(), __func__,
+              [self, fetcher]() {
+#ifdef DEBUG_DICT
+                printf("***** Assigned from content preferences |%s|\n",
+                       DictionariesToString(fetcher->mDictionaries).Data());
+#endif
+                // We take an early exit here, so let's not forget to clear
+                // the word list.
+                self->DeleteSuggestedWordList();
+
+                self->EndUpdateDictionary();
+                if (fetcher->mCallback) {
+                  fetcher->mCallback->EditorSpellCheckDone();
+                }
+              },
+              [self, fetcher](nsresult aError) {
+                if (aError == NS_ERROR_ABORT) {
+                  return;
+                }
+                // May be dictionary was uninstalled ?
+                // Clear the content preference and continue.
+                ClearCurrentDictionaries(self->mEditor);
+
+                // Priority 2 or later will handled by the following
+                self->SetFallbackDictionary(fetcher);
+              });
+      return NS_OK;
+    }
+  }
+  SetFallbackDictionary(aFetcher);
+  return NS_OK;
+}
+
+void EditorSpellCheck::SetDictionarySucceeded(DictionaryFetcher* aFetcher) {
+  DeleteSuggestedWordList();
+  EndUpdateDictionary();
+  if (aFetcher->mCallback) {
+    aFetcher->mCallback->EditorSpellCheckDone();
+  }
+}
+
+void EditorSpellCheck::SetFallbackDictionary(DictionaryFetcher* aFetcher) {
+  MOZ_ASSERT(mUpdateDictionaryRunning);
+
+  AutoTArray<nsCString, 6> tryDictList;
+
+  // We obtain a list of available dictionaries.
+  AutoTArray<nsCString, 8> dictList;
+  nsresult rv = mSpellChecker->GetDictionaryList(&dictList);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    EndUpdateDictionary();
+    if (aFetcher->mCallback) {
+      aFetcher->mCallback->EditorSpellCheckDone();
+    }
+    return;
+  }
+
+  // Priority 2:
+  // After checking the content preferences, we use the languages of the element
+  // or document.
+
+  // Get the preference value.
+  nsAutoCString prefDictionariesAsString;
+  Preferences::GetLocalizedCString("spellchecker.dictionary",
+                                   prefDictionariesAsString);
+  nsTArray<nsCString> prefDictionaries;
+  StringToDictionaries(prefDictionariesAsString, prefDictionaries);
+
+  nsAutoCString appLocaleStr;
+  // We pick one dictionary for every language that the element or document
+  // indicates it contains.
+  for (const auto& dictName : mPreferredLangs) {
+    // RFC 5646 explicitly states that matches should be case-insensitive.
+    if (BuildDictionaryList(dictName, dictList, DICT_COMPARE_CASE_INSENSITIVE,
+                            tryDictList)) {
+#ifdef DEBUG_DICT
+      printf("***** Trying from element/doc |%s| \n", dictName.get());
+#endif
+      continue;
+    }
+
+    // Required dictionary was not available. Try to get a dictionary
+    // matching at least language part of dictName.
+    mozilla::intl::Locale loc;
+    if (mozilla::intl::LocaleParser::TryParse(dictName, loc).isOk() &&
+        loc.Canonicalize().isOk()) {
+      Span<const char> language = loc.Language().Span();
+      nsAutoCString langCode(language.data(), language.size());
+
+      // Try dictionary.spellchecker preference, if it starts with langCode,
+      // so we don't just get any random dictionary matching the language.
+      bool didAppend = false;
+      for (const auto& dictionary : prefDictionaries) {
+        if (nsStyleUtil::DashMatchCompare(NS_ConvertUTF8toUTF16(dictionary),
+                                          NS_ConvertUTF8toUTF16(langCode),
+                                          nsTDefaultStringComparator)) {
+#ifdef DEBUG_DICT
+          printf(
+              "***** Trying preference value |%s| since it matches language "
+              "code\n",
+              dictionary.Data());
+#endif
+          if (BuildDictionaryList(dictionary, dictList,
+                                  DICT_COMPARE_CASE_INSENSITIVE, tryDictList)) {
+            didAppend = true;
+            break;
+          }
+        }
+      }
+      if (didAppend) {
+        continue;
+      }
+
+      // Use the application locale dictionary when the required language
+      // equals applocation locale language.
+      LocaleService::GetInstance()->GetAppLocaleAsBCP47(appLocaleStr);
+      if (!appLocaleStr.IsEmpty()) {
+        mozilla::intl::Locale appLoc;
+        auto result =
+            mozilla::intl::LocaleParser::TryParse(appLocaleStr, appLoc);
+        if (result.isOk() && appLoc.Canonicalize().isOk() &&
+            loc.Language().Span() == appLoc.Language().Span()) {
+          if (BuildDictionaryList(appLocaleStr, dictList,
+                                  DICT_COMPARE_CASE_INSENSITIVE, tryDictList)) {
+            continue;
+          }
+        }
+      }
+
+      // Use the system locale dictionary when the required language equlas
+      // system locale language.
+      nsAutoCString sysLocaleStr;
+      OSPreferences::GetInstance()->GetSystemLocale(sysLocaleStr);
+      if (!sysLocaleStr.IsEmpty()) {
+        mozilla::intl::Locale sysLoc;
+        auto result =
+            mozilla::intl::LocaleParser::TryParse(sysLocaleStr, sysLoc);
+        if (result.isOk() && sysLoc.Canonicalize().isOk() &&
+            loc.Language().Span() == sysLoc.Language().Span()) {
+          if (BuildDictionaryList(sysLocaleStr, dictList,
+                                  DICT_COMPARE_CASE_INSENSITIVE, tryDictList)) {
+            continue;
+          }
+        }
+      }
+
+      // Use any dictionary with the required language.
+#ifdef DEBUG_DICT
+      printf("***** Trying to find match for language code |%s|\n",
+             langCode.get());
+#endif
+      BuildDictionaryList(langCode, dictList, DICT_COMPARE_DASHMATCH,
+                          tryDictList);
+    }
+  }
+
+  RefPtr<EditorSpellCheck> self = this;
+  RefPtr<DictionaryFetcher> fetcher = aFetcher;
+  RefPtr<GenericPromise> promise;
+
+  if (tryDictList.IsEmpty()) {
+    // Proceed to priority 3 if the list of dictionaries is empty.
+    promise = GenericPromise::CreateAndReject(NS_ERROR_INVALID_ARG, __func__);
+  } else {
+    promise = mSpellChecker->SetCurrentDictionaries(tryDictList);
+  }
+
+  // If an error was thrown while setting the dictionary, just
+  // fail silently so that the spellchecker dialog is allowed to come
+  // up. The user can manually reset the language to their choice on
+  // the dialog if it is wrong.
+  promise->Then(
+      GetMainThreadSerialEventTarget(), __func__,
+      [self, fetcher]() { self->SetDictionarySucceeded(fetcher); },
+      [prefDictionaries = prefDictionaries.Clone(), dictList = dictList.Clone(),
+       self, fetcher]() {
+        // Build tryDictList with dictionaries for priorities 4 through 7.
+        // We'll use this list if there is no user preference or trying
+        // the user preference fails.
+        AutoTArray<nsCString, 6> tryDictList;
+
+        // Priority 4:
+        // As next fallback, try the current locale.
+        nsAutoCString appLocaleStr;
+        LocaleService::GetInstance()->GetAppLocaleAsBCP47(appLocaleStr);
+#ifdef DEBUG_DICT
+        printf("***** Trying locale |%s|\n", appLocaleStr.get());
+#endif
+        self->BuildDictionaryList(appLocaleStr, dictList,
+                                  DICT_COMPARE_CASE_INSENSITIVE, tryDictList);
+
+        // Priority 5:
+        // If we have a current dictionary and we don't have no item in try
+        // list, don't try anything else.
+        nsTArray<nsCString> currentDictionaries;
+        self->GetCurrentDictionaries(currentDictionaries);
+        if (!currentDictionaries.IsEmpty() && tryDictList.IsEmpty()) {
+#ifdef DEBUG_DICT
+          printf("***** Retrieved current dict |%s|\n",
+                 DictionariesToString(currentDictionaries).Data());
+#endif
+          self->EndUpdateDictionary();
+          if (fetcher->mCallback) {
+            fetcher->mCallback->EditorSpellCheckDone();
+          }
+          return;
+        }
+
+        // Priority 6:
+        // Try to get current dictionary from environment variable LANG.
+        // LANG = language[_territory][.charset]
+        char* env_lang = getenv("LANG");
+        if (env_lang) {
+          nsAutoCString lang(env_lang);
+          // Strip trailing charset, if there is any.
+          int32_t dot_pos = lang.FindChar('.');
+          if (dot_pos != -1) {
+            lang = Substring(lang, 0, dot_pos);
+          }
+
+          int32_t underScore = lang.FindChar('_');
+          if (underScore != -1) {
+            lang.Replace(underScore, 1, '-');
+#ifdef DEBUG_DICT
+            printf("***** Trying LANG from environment |%s|\n", lang.get());
+#endif
+            self->BuildDictionaryList(
+                lang, dictList, DICT_COMPARE_CASE_INSENSITIVE, tryDictList);
+          }
+        }
+
+        // Priority 7:
+        // If it does not work, pick the first one.
+        if (!dictList.IsEmpty()) {
+          self->BuildDictionaryList(dictList[0], dictList, DICT_NORMAL_COMPARE,
+                                    tryDictList);
+#ifdef DEBUG_DICT
+          printf("***** Trying first of list |%s|\n", dictList[0].get());
+#endif
+        }
+
+        // Priority 3:
+        // If the document didn't supply a dictionary or the setting
+        // failed, try the user preference next.
+        if (!prefDictionaries.IsEmpty()) {
+          self->mSpellChecker->SetCurrentDictionaries(prefDictionaries)
+              ->Then(
+                  GetMainThreadSerialEventTarget(), __func__,
+                  [self, fetcher]() { self->SetDictionarySucceeded(fetcher); },
+                  // Priority 3 failed, we'll use the list we built of
+                  // priorities 4 to 7.
+                  [tryDictList = tryDictList.Clone(), self, fetcher]() {
+                    self->mSpellChecker
+                        ->SetCurrentDictionaryFromList(tryDictList)
+                        ->Then(GetMainThreadSerialEventTarget(), __func__,
+                               [self, fetcher]() {
+                                 self->SetDictionarySucceeded(fetcher);
+                               });
+                  });
+        } else {
+          // We don't have a user preference, so we'll try the list we
+          // built of priorities 4 to 7.
+          self->mSpellChecker->SetCurrentDictionaryFromList(tryDictList)
+              ->Then(
+                  GetMainThreadSerialEventTarget(), __func__,
+                  [self, fetcher]() { self->SetDictionarySucceeded(fetcher); });
+        }
+      });
+}
+
+}  // namespace mozilla
diff --git a/editor/spellchecker/EditorSpellCheck.h b/editor/spellchecker/EditorSpellCheck.h
new file mode 100644
index 0000000000..d9de5d9d40
--- /dev/null
+++ b/editor/spellchecker/EditorSpellCheck.h
@@ -0,0 +1,99 @@
+/* -*- Mode: C++; tab-width: 2; 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 mozilla_EditorSpellCheck_h
+#define mozilla_EditorSpellCheck_h
+
+#include "mozilla/mozSpellChecker.h"  // for mozilla::CheckWordPromise
+#include "nsCOMPtr.h"                 // for nsCOMPtr
+#include "nsCycleCollectionParticipant.h"
+#include "nsIEditorSpellCheck.h"  // for NS_DECL_NSIEDITORSPELLCHECK, etc
+#include "nsISupportsImpl.h"
+#include "nsString.h"  // for nsString
+#include "nsTArray.h"  // for nsTArray
+#include "nscore.h"    // for nsresult
+
+class mozSpellChecker;
+class nsIEditor;
+
+namespace mozilla {
+
+class DictionaryFetcher;
+class EditorBase;
+
+enum dictCompare {
+  DICT_NORMAL_COMPARE,
+  DICT_COMPARE_CASE_INSENSITIVE,
+  DICT_COMPARE_DASHMATCH
+};
+
+class EditorSpellCheck final : public nsIEditorSpellCheck {
+  friend class DictionaryFetcher;
+
+ public:
+  EditorSpellCheck();
+
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_CLASS(EditorSpellCheck)
+
+  /* Declare all methods in the nsIEditorSpellCheck interface */
+  NS_DECL_NSIEDITORSPELLCHECK
+
+  mozSpellChecker* GetSpellChecker();
+
+  /**
+   * Like CheckCurrentWord, checks the word you give it, returning true via
+   * promise if it's misspelled.
+   * This is faster than CheckCurrentWord because it does not compute
+   * any suggestions.
+   *
+   * Watch out: this does not clear any suggestions left over from previous
+   * calls to CheckCurrentWord, so there may be suggestions, but they will be
+   * invalid.
+   */
+  RefPtr<mozilla::CheckWordPromise> CheckCurrentWordsNoSuggest(
+      const nsTArray<nsString>& aSuggestedWords);
+
+ protected:
+  virtual ~EditorSpellCheck();
+
+  RefPtr<mozSpellChecker> mSpellChecker;
+  RefPtr<EditorBase> mEditor;
+
+  nsTArray<nsString> mSuggestedWordList;
+
+  // these are the words in the current personal dictionary,
+  // GetPersonalDictionary must be called to load them.
+  nsTArray<nsString> mDictionaryList;
+
+  nsTArray<nsCString> mPreferredLangs;
+
+  uint32_t mTxtSrvFilterType;
+  int32_t mSuggestedWordIndex;
+  int32_t mDictionaryIndex;
+  uint32_t mDictionaryFetcherGroup;
+
+  bool mUpdateDictionaryRunning;
+
+  nsresult DeleteSuggestedWordList();
+
+  bool BuildDictionaryList(const nsACString& aDictName,
+                           const nsTArray<nsCString>& aDictList,
+                           enum dictCompare aCompareType,
+                           nsTArray<nsCString>& aOutList);
+
+  nsresult DictionaryFetched(DictionaryFetcher* aFetchState);
+
+  void SetDictionarySucceeded(DictionaryFetcher* aFetcher);
+  void SetFallbackDictionary(DictionaryFetcher* aFetcher);
+
+ public:
+  void BeginUpdateDictionary() { mUpdateDictionaryRunning = true; }
+  void EndUpdateDictionary() { mUpdateDictionaryRunning = false; }
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_EditorSpellCheck_h
diff --git a/editor/spellchecker/FilteredContentIterator.cpp b/editor/spellchecker/FilteredContentIterator.cpp
new file mode 100644
index 0000000000..b0bfcd508a
--- /dev/null
+++ b/editor/spellchecker/FilteredContentIterator.cpp
@@ -0,0 +1,398 @@
+/* -*- Mode: C++; tab-width: 2; 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 "FilteredContentIterator.h"
+
+#include <utility>
+
+#include "mozilla/ContentIterator.h"
+#include "mozilla/dom/AbstractRange.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/mozalloc.h"
+#include "nsAtom.h"
+#include "nsComponentManagerUtils.h"
+#include "nsComposeTxtSrvFilter.h"
+#include "nsContentUtils.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsIContent.h"
+#include "nsINode.h"
+#include "nsISupports.h"
+#include "nsISupportsUtils.h"
+#include "nsRange.h"
+
+namespace mozilla {
+
+using namespace dom;
+
+FilteredContentIterator::FilteredContentIterator(
+    UniquePtr<nsComposeTxtSrvFilter> aFilter)
+    : mCurrentIterator(nullptr),
+      mFilter(std::move(aFilter)),
+      mDidSkip(false),
+      mIsOutOfRange(false),
+      mDirection(eDirNotSet) {}
+
+FilteredContentIterator::~FilteredContentIterator() {}
+
+NS_IMPL_CYCLE_COLLECTION(FilteredContentIterator, mPostIterator, mPreIterator,
+                         mRange)
+
+nsresult FilteredContentIterator::Init(nsINode* aRoot) {
+  NS_ENSURE_ARG_POINTER(aRoot);
+  mIsOutOfRange = false;
+  mDirection = eForward;
+  mCurrentIterator = &mPreIterator;
+
+  mRange = nsRange::Create(aRoot);
+  mRange->SelectNode(*aRoot, IgnoreErrors());
+
+  nsresult rv = mPreIterator.Init(mRange);
+  NS_ENSURE_SUCCESS(rv, rv);
+  return mPostIterator.Init(mRange);
+}
+
+nsresult FilteredContentIterator::Init(const AbstractRange* aAbstractRange) {
+  if (NS_WARN_IF(!aAbstractRange)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  if (NS_WARN_IF(!aAbstractRange->IsPositioned())) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  mRange = nsRange::Create(aAbstractRange, IgnoreErrors());
+  if (NS_WARN_IF(!mRange)) {
+    return NS_ERROR_FAILURE;
+  }
+  return InitWithRange();
+}
+
+nsresult FilteredContentIterator::Init(nsINode* aStartContainer,
+                                       uint32_t aStartOffset,
+                                       nsINode* aEndContainer,
+                                       uint32_t aEndOffset) {
+  return Init(RawRangeBoundary(aStartContainer, aStartOffset),
+              RawRangeBoundary(aEndContainer, aEndOffset));
+}
+
+nsresult FilteredContentIterator::Init(const RawRangeBoundary& aStartBoundary,
+                                       const RawRangeBoundary& aEndBoundary) {
+  RefPtr<nsRange> range =
+      nsRange::Create(aStartBoundary, aEndBoundary, IgnoreErrors());
+  if (NS_WARN_IF(!range) || NS_WARN_IF(!range->IsPositioned())) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  MOZ_ASSERT(range->StartRef() == aStartBoundary);
+  MOZ_ASSERT(range->EndRef() == aEndBoundary);
+
+  mRange = std::move(range);
+
+  return InitWithRange();
+}
+
+nsresult FilteredContentIterator::InitWithRange() {
+  MOZ_ASSERT(mRange);
+  MOZ_ASSERT(mRange->IsPositioned());
+
+  mIsOutOfRange = false;
+  mDirection = eForward;
+  mCurrentIterator = &mPreIterator;
+
+  nsresult rv = mPreIterator.Init(mRange);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  return mPostIterator.Init(mRange);
+}
+
+nsresult FilteredContentIterator::SwitchDirections(bool aChangeToForward) {
+  nsINode* node = mCurrentIterator->GetCurrentNode();
+
+  if (aChangeToForward) {
+    mCurrentIterator = &mPreIterator;
+    mDirection = eForward;
+  } else {
+    mCurrentIterator = &mPostIterator;
+    mDirection = eBackward;
+  }
+
+  if (node) {
+    nsresult rv = mCurrentIterator->PositionAt(node);
+    if (NS_FAILED(rv)) {
+      mIsOutOfRange = true;
+      return rv;
+    }
+  }
+  return NS_OK;
+}
+
+void FilteredContentIterator::First() {
+  if (!mCurrentIterator) {
+    NS_ERROR("Missing iterator!");
+
+    return;
+  }
+
+  // If we are switching directions then
+  // we need to switch how we process the nodes
+  if (mDirection != eForward) {
+    mCurrentIterator = &mPreIterator;
+    mDirection = eForward;
+    mIsOutOfRange = false;
+  }
+
+  mCurrentIterator->First();
+
+  if (mCurrentIterator->IsDone()) {
+    return;
+  }
+
+  nsINode* currentNode = mCurrentIterator->GetCurrentNode();
+
+  bool didCross;
+  CheckAdvNode(currentNode, didCross, eForward);
+}
+
+void FilteredContentIterator::Last() {
+  if (!mCurrentIterator) {
+    NS_ERROR("Missing iterator!");
+
+    return;
+  }
+
+  // If we are switching directions then
+  // we need to switch how we process the nodes
+  if (mDirection != eBackward) {
+    mCurrentIterator = &mPostIterator;
+    mDirection = eBackward;
+    mIsOutOfRange = false;
+  }
+
+  mCurrentIterator->Last();
+
+  if (mCurrentIterator->IsDone()) {
+    return;
+  }
+
+  nsINode* currentNode = mCurrentIterator->GetCurrentNode();
+
+  bool didCross;
+  CheckAdvNode(currentNode, didCross, eBackward);
+}
+
+///////////////////////////////////////////////////////////////////////////
+// ContentIsInTraversalRange: returns true if content is visited during
+// the traversal of the range in the specified mode.
+//
+static bool ContentIsInTraversalRange(nsIContent* aContent, bool aIsPreMode,
+                                      nsINode* aStartContainer,
+                                      int32_t aStartOffset,
+                                      nsINode* aEndContainer,
+                                      int32_t aEndOffset) {
+  NS_ENSURE_TRUE(aStartContainer && aEndContainer && aContent, false);
+
+  nsIContent* parentContent = aContent->GetParent();
+  if (MOZ_UNLIKELY(NS_WARN_IF(!parentContent))) {
+    return false;
+  }
+  Maybe<uint32_t> offsetInParent = parentContent->ComputeIndexOf(aContent);
+  NS_WARNING_ASSERTION(
+      offsetInParent.isSome(),
+      "Content is not in the parent, is this called during a DOM mutation?");
+  if (MOZ_UNLIKELY(NS_WARN_IF(offsetInParent.isNothing()))) {
+    return false;
+  }
+
+  if (!aIsPreMode) {
+    MOZ_ASSERT(*offsetInParent != UINT32_MAX);
+    ++(*offsetInParent);
+  }
+
+  const Maybe<int32_t> startRes = nsContentUtils::ComparePoints(
+      aStartContainer, aStartOffset, parentContent, *offsetInParent);
+  if (MOZ_UNLIKELY(NS_WARN_IF(!startRes))) {
+    return false;
+  }
+  const Maybe<int32_t> endRes = nsContentUtils::ComparePoints(
+      aEndContainer, aEndOffset, parentContent, *offsetInParent);
+  if (MOZ_UNLIKELY(NS_WARN_IF(!endRes))) {
+    return false;
+  }
+  return *startRes <= 0 && *endRes >= 0;
+}
+
+static bool ContentIsInTraversalRange(nsRange* aRange, nsIContent* aNextContent,
+                                      bool aIsPreMode) {
+  // XXXbz we have a caller below (in AdvanceNode) who passes null for
+  // aNextContent!
+  NS_ENSURE_TRUE(aNextContent && aRange, false);
+
+  return ContentIsInTraversalRange(
+      aNextContent, aIsPreMode, aRange->GetStartContainer(),
+      static_cast<int32_t>(aRange->StartOffset()), aRange->GetEndContainer(),
+      static_cast<int32_t>(aRange->EndOffset()));
+}
+
+// Helper function to advance to the next or previous node
+nsresult FilteredContentIterator::AdvanceNode(nsINode* aNode,
+                                              nsINode*& aNewNode,
+                                              eDirectionType aDir) {
+  nsCOMPtr<nsIContent> nextNode;
+  if (aDir == eForward) {
+    nextNode = aNode->GetNextSibling();
+  } else {
+    nextNode = aNode->GetPreviousSibling();
+  }
+
+  if (nextNode) {
+    // If we got here, that means we found the nxt/prv node
+    // make sure it is in our DOMRange
+    bool intersects =
+        ContentIsInTraversalRange(mRange, nextNode, aDir == eForward);
+    if (intersects) {
+      aNewNode = nextNode;
+      NS_ADDREF(aNewNode);
+      return NS_OK;
+    }
+  } else {
+    // The next node was null so we need to walk up the parent(s)
+    nsCOMPtr<nsINode> parent = aNode->GetParentNode();
+    NS_ASSERTION(parent, "parent can't be nullptr");
+
+    // Make sure the parent is in the DOMRange before going further
+    // XXXbz why are we passing nextNode, not the parent???  If this gets fixed,
+    // then ContentIsInTraversalRange can stop null-checking its second arg.
+    bool intersects =
+        ContentIsInTraversalRange(mRange, nextNode, aDir == eForward);
+    if (intersects) {
+      // Now find the nxt/prv node after/before this node
+      nsresult rv = AdvanceNode(parent, aNewNode, aDir);
+      if (NS_SUCCEEDED(rv) && aNewNode) {
+        return NS_OK;
+      }
+    }
+  }
+
+  // if we get here it pretty much means
+  // we went out of the DOM Range
+  mIsOutOfRange = true;
+
+  return NS_ERROR_FAILURE;
+}
+
+// Helper function to see if the next/prev node should be skipped
+void FilteredContentIterator::CheckAdvNode(nsINode* aNode, bool& aDidSkip,
+                                           eDirectionType aDir) {
+  aDidSkip = false;
+  mIsOutOfRange = false;
+
+  if (aNode && mFilter) {
+    nsCOMPtr<nsINode> currentNode = aNode;
+    while (1) {
+      if (mFilter->Skip(aNode)) {
+        aDidSkip = true;
+        // Get the next/prev node and then
+        // see if we should skip that
+        nsCOMPtr<nsINode> advNode;
+        nsresult rv = AdvanceNode(aNode, *getter_AddRefs(advNode), aDir);
+        if (NS_SUCCEEDED(rv) && advNode) {
+          aNode = advNode;
+        } else {
+          return;  // fell out of range
+        }
+      } else {
+        if (aNode != currentNode) {
+          nsCOMPtr<nsIContent> content(do_QueryInterface(aNode));
+          mCurrentIterator->PositionAt(content);
+        }
+        return;  // found something
+      }
+    }
+  }
+}
+
+void FilteredContentIterator::Next() {
+  if (mIsOutOfRange || !mCurrentIterator) {
+    NS_ASSERTION(mCurrentIterator, "Missing iterator!");
+
+    return;
+  }
+
+  // If we are switching directions then
+  // we need to switch how we process the nodes
+  if (mDirection != eForward) {
+    nsresult rv = SwitchDirections(true);
+    if (NS_FAILED(rv)) {
+      return;
+    }
+  }
+
+  mCurrentIterator->Next();
+
+  if (mCurrentIterator->IsDone()) {
+    return;
+  }
+
+  // If we can't get the current node then
+  // don't check to see if we can skip it
+  nsINode* currentNode = mCurrentIterator->GetCurrentNode();
+
+  CheckAdvNode(currentNode, mDidSkip, eForward);
+}
+
+void FilteredContentIterator::Prev() {
+  if (mIsOutOfRange || !mCurrentIterator) {
+    NS_ASSERTION(mCurrentIterator, "Missing iterator!");
+
+    return;
+  }
+
+  // If we are switching directions then
+  // we need to switch how we process the nodes
+  if (mDirection != eBackward) {
+    nsresult rv = SwitchDirections(false);
+    if (NS_FAILED(rv)) {
+      return;
+    }
+  }
+
+  mCurrentIterator->Prev();
+
+  if (mCurrentIterator->IsDone()) {
+    return;
+  }
+
+  // If we can't get the current node then
+  // don't check to see if we can skip it
+  nsINode* currentNode = mCurrentIterator->GetCurrentNode();
+
+  CheckAdvNode(currentNode, mDidSkip, eBackward);
+}
+
+nsINode* FilteredContentIterator::GetCurrentNode() {
+  if (mIsOutOfRange || !mCurrentIterator) {
+    return nullptr;
+  }
+
+  return mCurrentIterator->GetCurrentNode();
+}
+
+bool FilteredContentIterator::IsDone() {
+  if (mIsOutOfRange || !mCurrentIterator) {
+    return true;
+  }
+
+  return mCurrentIterator->IsDone();
+}
+
+nsresult FilteredContentIterator::PositionAt(nsINode* aCurNode) {
+  NS_ENSURE_TRUE(mCurrentIterator, NS_ERROR_FAILURE);
+  mIsOutOfRange = false;
+  return mCurrentIterator->PositionAt(aCurNode);
+}
+
+}  // namespace mozilla
diff --git a/editor/spellchecker/FilteredContentIterator.h b/editor/spellchecker/FilteredContentIterator.h
new file mode 100644
index 0000000000..a6fee6c150
--- /dev/null
+++ b/editor/spellchecker/FilteredContentIterator.h
@@ -0,0 +1,82 @@
+/* -*- Mode: C++; tab-width: 2; 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 FilteredContentIterator_h
+#define FilteredContentIterator_h
+
+#include "nsComposeTxtSrvFilter.h"
+#include "nsCOMPtr.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsISupportsImpl.h"
+#include "nscore.h"
+#include "mozilla/ContentIterator.h"
+#include "mozilla/UniquePtr.h"
+
+class nsAtom;
+class nsINode;
+class nsRange;
+
+namespace mozilla {
+
+namespace dom {
+class AbstractRange;
+}
+
+class FilteredContentIterator final {
+ public:
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(FilteredContentIterator)
+  NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS(FilteredContentIterator)
+
+  explicit FilteredContentIterator(UniquePtr<nsComposeTxtSrvFilter> aFilter);
+
+  nsresult Init(nsINode* aRoot);
+  nsresult Init(const dom::AbstractRange* aAbstractRange);
+  nsresult Init(nsINode* aStartContainer, uint32_t aStartOffset,
+                nsINode* aEndContainer, uint32_t aEndOffset);
+  nsresult Init(const RawRangeBoundary& aStartBoundary,
+                const RawRangeBoundary& aEndBoundary);
+  void First();
+  void Last();
+  void Next();
+  void Prev();
+  nsINode* GetCurrentNode();
+  bool IsDone();
+  nsresult PositionAt(nsINode* aCurNode);
+
+  /* Helpers */
+  bool DidSkip() { return mDidSkip; }
+  void ClearDidSkip() { mDidSkip = false; }
+
+ protected:
+  FilteredContentIterator()
+      : mDidSkip(false), mIsOutOfRange(false), mDirection{eDirNotSet} {}
+
+  virtual ~FilteredContentIterator();
+
+  /**
+   * Callers must guarantee that mRange isn't nullptr and it's positioned.
+   */
+  nsresult InitWithRange();
+
+  // enum to give us the direction
+  typedef enum { eDirNotSet, eForward, eBackward } eDirectionType;
+  nsresult AdvanceNode(nsINode* aNode, nsINode*& aNewNode, eDirectionType aDir);
+  void CheckAdvNode(nsINode* aNode, bool& aDidSkip, eDirectionType aDir);
+  nsresult SwitchDirections(bool aChangeToForward);
+
+  SafeContentIteratorBase* MOZ_NON_OWNING_REF mCurrentIterator;
+  PostContentIterator mPostIterator;
+  PreContentIterator mPreIterator;
+
+  UniquePtr<nsComposeTxtSrvFilter> mFilter;
+  RefPtr<nsRange> mRange;
+  bool mDidSkip;
+  bool mIsOutOfRange;
+  eDirectionType mDirection;
+};
+
+}  // namespace mozilla
+
+#endif  // #ifndef FilteredContentIterator_h
diff --git a/editor/spellchecker/TextServicesDocument.cpp b/editor/spellchecker/TextServicesDocument.cpp
new file mode 100644
index 0000000000..1417cf79ae
--- /dev/null
+++ b/editor/spellchecker/TextServicesDocument.cpp
@@ -0,0 +1,2787 @@
+/* -*- Mode: C++; tab-width: 2; 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 "TextServicesDocument.h"
+
+#include "EditorBase.h"               // for EditorBase
+#include "EditorUtils.h"              // for AutoTransactionBatchExternal
+#include "FilteredContentIterator.h"  // for FilteredContentIterator
+#include "HTMLEditHelpers.h"          // for BlockInlineCheck
+#include "HTMLEditUtils.h"            // for HTMLEditUtils
+
+#include "mozilla/Assertions.h"    // for MOZ_ASSERT, etc
+#include "mozilla/IntegerRange.h"  // for IntegerRange
+#include "mozilla/mozalloc.h"      // for operator new, etc
+#include "mozilla/OwningNonNull.h"
+#include "mozilla/UniquePtr.h"          // for UniquePtr
+#include "mozilla/dom/AbstractRange.h"  // for AbstractRange
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/Selection.h"
+#include "mozilla/dom/StaticRange.h"  // for StaticRange
+#include "mozilla/dom/Text.h"
+#include "mozilla/intl/WordBreaker.h"  // for WordRange, WordBreaker
+
+#include "nsAString.h"       // for nsAString::Length, etc
+#include "nsContentUtils.h"  // for nsContentUtils
+#include "nsComposeTxtSrvFilter.h"
+#include "nsDebug.h"                 // for NS_ENSURE_TRUE, etc
+#include "nsDependentSubstring.h"    // for Substring
+#include "nsError.h"                 // for NS_OK, NS_ERROR_FAILURE, etc
+#include "nsGenericHTMLElement.h"    // for nsGenericHTMLElement
+#include "nsIContent.h"              // for nsIContent, etc
+#include "nsID.h"                    // for NS_GET_IID
+#include "nsIEditor.h"               // for nsIEditor, etc
+#include "nsIEditorSpellCheck.h"     // for nsIEditorSpellCheck, etc
+#include "nsINode.h"                 // for nsINode
+#include "nsISelectionController.h"  // for nsISelectionController, etc
+#include "nsISupports.h"             // for nsISupports
+#include "nsISupportsUtils.h"        // for NS_IF_ADDREF, NS_ADDREF, etc
+#include "nsRange.h"                 // for nsRange
+#include "nsString.h"                // for nsString, nsAutoString
+#include "nscore.h"                  // for nsresult, NS_IMETHODIMP, etc
+
+namespace mozilla {
+
+using namespace dom;
+
+/**
+ * OffsetEntry manages a range in a text node.  It stores 2 offset values,
+ * one is offset in the text node, the other is offset in all text in
+ * the ancestor block of the text node.  And the length is managing length
+ * in the text node, starting from the offset in text node.
+ * In other words, a text node may be managed by multiple instances of this
+ * class.
+ */
+class OffsetEntry final {
+ public:
+  OffsetEntry() = delete;
+
+  /**
+   * @param aTextNode   The text node which will be manged by the instance.
+   * @param aOffsetInTextInBlock
+   *                    Start offset in the text node which will be managed by
+   *                    the instance.
+   * @param aLength     Length in the text node which will be managed by the
+   *                    instance.
+   */
+  OffsetEntry(Text& aTextNode, uint32_t aOffsetInTextInBlock, uint32_t aLength)
+      : mTextNode(aTextNode),
+        mOffsetInTextNode(0),
+        mOffsetInTextInBlock(aOffsetInTextInBlock),
+        mLength(aLength),
+        mIsInsertedText(false),
+        mIsValid(true) {}
+
+  /**
+   * EndOffsetInTextNode() returns end offset in the text node, which is
+   * managed by the instance.
+   */
+  uint32_t EndOffsetInTextNode() const { return mOffsetInTextNode + mLength; }
+
+  /**
+   * OffsetInTextNodeIsInRangeOrEndOffset() checks whether the offset in
+   * the text node is managed by the instance or not.
+   */
+  bool OffsetInTextNodeIsInRangeOrEndOffset(uint32_t aOffsetInTextNode) const {
+    return aOffsetInTextNode >= mOffsetInTextNode &&
+           aOffsetInTextNode <= EndOffsetInTextNode();
+  }
+
+  /**
+   * EndOffsetInTextInBlock() returns end offset in the all text in ancestor
+   * block of the text node, which is managed by the instance.
+   */
+  uint32_t EndOffsetInTextInBlock() const {
+    return mOffsetInTextInBlock + mLength;
+  }
+
+  /**
+   * OffsetInTextNodeIsInRangeOrEndOffset() checks whether the offset in
+   * the all text in ancestor block of the text node is managed by the instance
+   * or not.
+   */
+  bool OffsetInTextInBlockIsInRangeOrEndOffset(
+      uint32_t aOffsetInTextInBlock) const {
+    return aOffsetInTextInBlock >= mOffsetInTextInBlock &&
+           aOffsetInTextInBlock <= EndOffsetInTextInBlock();
+  }
+
+  OwningNonNull<Text> mTextNode;
+  uint32_t mOffsetInTextNode;
+  // Offset in all text in the closest ancestor block of mTextNode.
+  uint32_t mOffsetInTextInBlock;
+  uint32_t mLength;
+  bool mIsInsertedText;
+  bool mIsValid;
+};
+
+template <typename ElementType>
+struct MOZ_STACK_CLASS ArrayLengthMutationGuard final {
+  ArrayLengthMutationGuard() = delete;
+  explicit ArrayLengthMutationGuard(const nsTArray<ElementType>& aArray)
+      : mArray(aArray), mOldLength(aArray.Length()) {}
+  ~ArrayLengthMutationGuard() {
+    if (mArray.Length() != mOldLength) {
+      MOZ_CRASH("The array length was changed unexpectedly");
+    }
+  }
+
+ private:
+  const nsTArray<ElementType>& mArray;
+  size_t mOldLength;
+};
+
+#define LockOffsetEntryArrayLengthInDebugBuild(aName, aArray)               \
+  DebugOnly<ArrayLengthMutationGuard<UniquePtr<OffsetEntry>>> const aName = \
+      ArrayLengthMutationGuard<UniquePtr<OffsetEntry>>(aArray);
+
+TextServicesDocument::TextServicesDocument()
+    : mTxtSvcFilterType(0), mIteratorStatus(IteratorStatus::eDone) {}
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TextServicesDocument)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TextServicesDocument)
+
+NS_INTERFACE_MAP_BEGIN(TextServicesDocument)
+  NS_INTERFACE_MAP_ENTRY(nsIEditActionListener)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIEditActionListener)
+  NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(TextServicesDocument)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION(TextServicesDocument, mDocument, mSelCon, mEditorBase,
+                         mFilteredIter, mPrevTextBlock, mNextTextBlock, mExtent)
+
+nsresult TextServicesDocument::InitWithEditor(nsIEditor* aEditor) {
+  nsCOMPtr<nsISelectionController> selCon;
+
+  NS_ENSURE_TRUE(aEditor, NS_ERROR_NULL_POINTER);
+
+  // Check to see if we already have an mSelCon. If we do, it
+  // better be the same one the editor uses!
+
+  nsresult rv = aEditor->GetSelectionController(getter_AddRefs(selCon));
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (!selCon || (mSelCon && selCon != mSelCon)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (!mSelCon) {
+    mSelCon = selCon;
+  }
+
+  // Check to see if we already have an mDocument. If we do, it
+  // better be the same one the editor uses!
+
+  RefPtr<Document> doc = aEditor->AsEditorBase()->GetDocument();
+  if (!doc || (mDocument && doc != mDocument)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (!mDocument) {
+    mDocument = doc;
+
+    rv = CreateDocumentContentIterator(getter_AddRefs(mFilteredIter));
+
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    mIteratorStatus = IteratorStatus::eDone;
+
+    rv = FirstBlock();
+
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  mEditorBase = aEditor->AsEditorBase();
+
+  rv = aEditor->AddEditActionListener(this);
+
+  return rv;
+}
+
+nsresult TextServicesDocument::SetExtent(const AbstractRange* aAbstractRange) {
+  MOZ_ASSERT(aAbstractRange);
+
+  if (NS_WARN_IF(!mDocument)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // We need to store a copy of aAbstractRange since we don't know where it
+  // came from.
+  mExtent = nsRange::Create(aAbstractRange, IgnoreErrors());
+  if (NS_WARN_IF(!mExtent)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Create a new iterator based on our new extent range.
+  nsresult rv =
+      CreateFilteredContentIterator(mExtent, getter_AddRefs(mFilteredIter));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Now position the iterator at the start of the first block
+  // in the range.
+  mIteratorStatus = IteratorStatus::eDone;
+
+  rv = FirstBlock();
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "FirstBlock() failed");
+  return rv;
+}
+
+nsresult TextServicesDocument::ExpandRangeToWordBoundaries(
+    StaticRange* aStaticRange) {
+  MOZ_ASSERT(aStaticRange);
+
+  // Get the end points of the range.
+
+  nsCOMPtr<nsINode> rngStartNode, rngEndNode;
+  uint32_t rngStartOffset, rngEndOffset;
+
+  nsresult rv = GetRangeEndPoints(aStaticRange, getter_AddRefs(rngStartNode),
+                                  &rngStartOffset, getter_AddRefs(rngEndNode),
+                                  &rngEndOffset);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Create a content iterator based on the range.
+  RefPtr<FilteredContentIterator> filteredIter;
+  rv =
+      CreateFilteredContentIterator(aStaticRange, getter_AddRefs(filteredIter));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Find the first text node in the range.
+  IteratorStatus iterStatus = IteratorStatus::eDone;
+  rv = FirstTextNode(filteredIter, &iterStatus);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (iterStatus == IteratorStatus::eDone) {
+    // No text was found so there's no adjustment necessary!
+    return NS_OK;
+  }
+
+  nsINode* firstText = filteredIter->GetCurrentNode();
+  if (NS_WARN_IF(!firstText)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Find the last text node in the range.
+
+  rv = LastTextNode(filteredIter, &iterStatus);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (iterStatus == IteratorStatus::eDone) {
+    // We should never get here because a first text block
+    // was found above.
+    NS_ASSERTION(false, "Found a first without a last!");
+    return NS_ERROR_FAILURE;
+  }
+
+  nsINode* lastText = filteredIter->GetCurrentNode();
+  if (NS_WARN_IF(!lastText)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Now make sure our end points are in terms of text nodes in the range!
+
+  if (rngStartNode != firstText) {
+    // The range includes the start of the first text node!
+    rngStartNode = firstText;
+    rngStartOffset = 0;
+  }
+
+  if (rngEndNode != lastText) {
+    // The range includes the end of the last text node!
+    rngEndNode = lastText;
+    rngEndOffset = lastText->Length();
+  }
+
+  // Create a doc iterator so that we can scan beyond
+  // the bounds of the extent range.
+
+  RefPtr<FilteredContentIterator> docFilteredIter;
+  rv = CreateDocumentContentIterator(getter_AddRefs(docFilteredIter));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Grab all the text in the block containing our
+  // first text node.
+  rv = docFilteredIter->PositionAt(firstText);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  iterStatus = IteratorStatus::eValid;
+
+  OffsetEntryArray offsetTable;
+  nsAutoString blockStr;
+  Result<IteratorStatus, nsresult> result = offsetTable.Init(
+      *docFilteredIter, IteratorStatus::eValid, nullptr, &blockStr);
+  if (result.isErr()) {
+    return result.unwrapErr();
+  }
+
+  Result<EditorDOMRangeInTexts, nsresult> maybeWordRange =
+      offsetTable.FindWordRange(
+          blockStr, EditorRawDOMPoint(rngStartNode, rngStartOffset));
+  offsetTable.Clear();
+  if (maybeWordRange.isErr()) {
+    NS_WARNING(
+        "TextServicesDocument::OffsetEntryArray::FindWordRange() failed");
+    return maybeWordRange.unwrapErr();
+  }
+  rngStartNode = maybeWordRange.inspect().StartRef().GetContainerAs<Text>();
+  rngStartOffset = maybeWordRange.inspect().StartRef().Offset();
+
+  // Grab all the text in the block containing our
+  // last text node.
+
+  rv = docFilteredIter->PositionAt(lastText);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  result = offsetTable.Init(*docFilteredIter, IteratorStatus::eValid, nullptr,
+                            &blockStr);
+  if (result.isErr()) {
+    return result.unwrapErr();
+  }
+
+  maybeWordRange = offsetTable.FindWordRange(
+      blockStr, EditorRawDOMPoint(rngEndNode, rngEndOffset));
+  offsetTable.Clear();
+  if (maybeWordRange.isErr()) {
+    NS_WARNING(
+        "TextServicesDocument::OffsetEntryArray::FindWordRange() failed");
+    return maybeWordRange.unwrapErr();
+  }
+
+  // To prevent expanding the range too much, we only change
+  // rngEndNode and rngEndOffset if it isn't already at the start of the
+  // word and isn't equivalent to rngStartNode and rngStartOffset.
+
+  if (rngEndNode !=
+          maybeWordRange.inspect().StartRef().GetContainerAs<Text>() ||
+      rngEndOffset != maybeWordRange.inspect().StartRef().Offset() ||
+      (rngEndNode == rngStartNode && rngEndOffset == rngStartOffset)) {
+    rngEndNode = maybeWordRange.inspect().EndRef().GetContainerAs<Text>();
+    rngEndOffset = maybeWordRange.inspect().EndRef().Offset();
+  }
+
+  // Now adjust the range so that it uses our new end points.
+  rv = aStaticRange->SetStartAndEnd(rngStartNode, rngStartOffset, rngEndNode,
+                                    rngEndOffset);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "Failed to update the given range");
+  return rv;
+}
+
+nsresult TextServicesDocument::SetFilterType(uint32_t aFilterType) {
+  mTxtSvcFilterType = aFilterType;
+
+  return NS_OK;
+}
+
+nsresult TextServicesDocument::GetCurrentTextBlock(nsAString& aStr) {
+  aStr.Truncate();
+
+  NS_ENSURE_TRUE(mFilteredIter, NS_ERROR_FAILURE);
+
+  Result<IteratorStatus, nsresult> result =
+      mOffsetTable.Init(*mFilteredIter, mIteratorStatus, mExtent, &aStr);
+  if (result.isErr()) {
+    NS_WARNING("OffsetEntryArray::Init() failed");
+    return result.unwrapErr();
+  }
+  mIteratorStatus = result.unwrap();
+  return NS_OK;
+}
+
+nsresult TextServicesDocument::FirstBlock() {
+  NS_ENSURE_TRUE(mFilteredIter, NS_ERROR_FAILURE);
+
+  nsresult rv = FirstTextNode(mFilteredIter, &mIteratorStatus);
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Keep track of prev and next blocks, just in case
+  // the text service blows away the current block.
+
+  if (mIteratorStatus == IteratorStatus::eValid) {
+    mPrevTextBlock = nullptr;
+    rv = GetFirstTextNodeInNextBlock(getter_AddRefs(mNextTextBlock));
+  } else {
+    // There's no text block in the document!
+
+    mPrevTextBlock = nullptr;
+    mNextTextBlock = nullptr;
+  }
+
+  // XXX Result of FirstTextNode() or GetFirstTextNodeInNextBlock().
+  return rv;
+}
+
+nsresult TextServicesDocument::LastSelectedBlock(
+    BlockSelectionStatus* aSelStatus, uint32_t* aSelOffset,
+    uint32_t* aSelLength) {
+  NS_ENSURE_TRUE(aSelStatus && aSelOffset && aSelLength, NS_ERROR_NULL_POINTER);
+
+  mIteratorStatus = IteratorStatus::eDone;
+
+  *aSelStatus = BlockSelectionStatus::eBlockNotFound;
+  *aSelOffset = *aSelLength = UINT32_MAX;
+
+  if (!mSelCon || !mFilteredIter) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<Selection> selection =
+      mSelCon->GetSelection(nsISelectionController::SELECTION_NORMAL);
+  if (NS_WARN_IF(!selection)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<const nsRange> range;
+  nsCOMPtr<nsINode> parent;
+
+  if (selection->IsCollapsed()) {
+    // We have a caret. Check if the caret is in a text node.
+    // If it is, make the text node's block the current block.
+    // If the caret isn't in a text node, search forwards in
+    // the document, till we find a text node.
+
+    range = selection->GetRangeAt(0);
+    if (!range) {
+      return NS_ERROR_FAILURE;
+    }
+
+    parent = range->GetStartContainer();
+    if (!parent) {
+      return NS_ERROR_FAILURE;
+    }
+
+    nsresult rv;
+    if (parent->IsText()) {
+      // The caret is in a text node. Find the beginning
+      // of the text block containing this text node and
+      // return.
+
+      rv = mFilteredIter->PositionAt(parent->AsText());
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      rv = FirstTextNodeInCurrentBlock(mFilteredIter);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      Result<IteratorStatus, nsresult> result =
+          mOffsetTable.Init(*mFilteredIter, IteratorStatus::eValid, mExtent);
+      if (result.isErr()) {
+        NS_WARNING("OffsetEntryArray::Init() failed");
+        mIteratorStatus = IteratorStatus::eValid;  // XXX
+        return result.unwrapErr();
+      }
+      mIteratorStatus = result.unwrap();
+
+      rv = GetSelection(aSelStatus, aSelOffset, aSelLength);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      if (*aSelStatus == BlockSelectionStatus::eBlockContains) {
+        rv = SetSelectionInternal(*aSelOffset, *aSelLength, false);
+      }
+    } else {
+      // The caret isn't in a text node. Create an iterator
+      // based on a range that extends from the current caret
+      // position to the end of the document, then walk forwards
+      // till you find a text node, then find the beginning of it's block.
+
+      range = CreateDocumentContentRootToNodeOffsetRange(
+          parent, range->StartOffset(), false);
+      if (NS_WARN_IF(!range)) {
+        return NS_ERROR_FAILURE;
+      }
+
+      if (range->Collapsed()) {
+        // If we get here, the range is collapsed because there is nothing after
+        // the caret! Just return NS_OK;
+        return NS_OK;
+      }
+
+      RefPtr<FilteredContentIterator> filteredIter;
+      rv = CreateFilteredContentIterator(range, getter_AddRefs(filteredIter));
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      filteredIter->First();
+
+      Text* textNode = nullptr;
+      for (; !filteredIter->IsDone(); filteredIter->Next()) {
+        nsINode* currentNode = filteredIter->GetCurrentNode();
+        if (currentNode->IsText()) {
+          textNode = currentNode->AsText();
+          break;
+        }
+      }
+
+      if (!textNode) {
+        return NS_OK;
+      }
+
+      rv = mFilteredIter->PositionAt(textNode);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      rv = FirstTextNodeInCurrentBlock(mFilteredIter);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      Result<IteratorStatus, nsresult> result = mOffsetTable.Init(
+          *mFilteredIter, IteratorStatus::eValid, mExtent, nullptr);
+      if (result.isErr()) {
+        NS_WARNING("OffsetEntryArray::Init() failed");
+        mIteratorStatus = IteratorStatus::eValid;  // XXX
+        return result.unwrapErr();
+      }
+      mIteratorStatus = result.inspect();
+
+      rv = GetSelection(aSelStatus, aSelOffset, aSelLength);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    }
+
+    // Result of SetSelectionInternal() in the |if| block or NS_OK.
+    return rv;
+  }
+
+  // If we get here, we have an uncollapsed selection!
+  // Look backwards through each range in the selection till you
+  // find the first text node. If you find one, find the
+  // beginning of its text block, and make it the current
+  // block.
+
+  const uint32_t rangeCount = selection->RangeCount();
+  MOZ_ASSERT(
+      rangeCount,
+      "Selection is not collapsed, so, the range count should be 1 or larger");
+
+  // XXX: We may need to add some code here to make sure
+  //      the ranges are sorted in document appearance order!
+
+  for (const uint32_t i : Reversed(IntegerRange(rangeCount))) {
+    MOZ_ASSERT(selection->RangeCount() == rangeCount);
+    range = selection->GetRangeAt(i);
+    if (MOZ_UNLIKELY(!range)) {
+      return NS_OK;  // XXX Really?
+    }
+
+    // Create an iterator for the range.
+
+    RefPtr<FilteredContentIterator> filteredIter;
+    nsresult rv =
+        CreateFilteredContentIterator(range, getter_AddRefs(filteredIter));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    filteredIter->Last();
+
+    // Now walk through the range till we find a text node.
+
+    for (; !filteredIter->IsDone(); filteredIter->Prev()) {
+      if (filteredIter->GetCurrentNode()->NodeType() == nsINode::TEXT_NODE) {
+        // We found a text node, so position the document's
+        // iterator at the beginning of the block, then get
+        // the selection in terms of the string offset.
+
+        nsresult rv = mFilteredIter->PositionAt(filteredIter->GetCurrentNode());
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+
+        rv = FirstTextNodeInCurrentBlock(mFilteredIter);
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+
+        mIteratorStatus = IteratorStatus::eValid;
+
+        Result<IteratorStatus, nsresult> result =
+            mOffsetTable.Init(*mFilteredIter, IteratorStatus::eValid, mExtent);
+        if (result.isErr()) {
+          NS_WARNING("OffsetEntryArray::Init() failed");
+          mIteratorStatus = IteratorStatus::eValid;  // XXX
+          return result.unwrapErr();
+        }
+        mIteratorStatus = result.unwrap();
+
+        return GetSelection(aSelStatus, aSelOffset, aSelLength);
+      }
+    }
+  }
+
+  // If we get here, we didn't find any text node in the selection!
+  // Create a range that extends from the end of the selection,
+  // to the end of the document, then iterate forwards through
+  // it till you find a text node!
+  range = rangeCount > 0 ? selection->GetRangeAt(rangeCount - 1) : nullptr;
+  if (!range) {
+    return NS_ERROR_FAILURE;
+  }
+
+  parent = range->GetEndContainer();
+  if (!parent) {
+    return NS_ERROR_FAILURE;
+  }
+
+  range = CreateDocumentContentRootToNodeOffsetRange(parent, range->EndOffset(),
+                                                     false);
+  if (NS_WARN_IF(!range)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (range->Collapsed()) {
+    // If we get here, the range is collapsed because there is nothing after
+    // the current selection! Just return NS_OK;
+    return NS_OK;
+  }
+
+  RefPtr<FilteredContentIterator> filteredIter;
+  nsresult rv =
+      CreateFilteredContentIterator(range, getter_AddRefs(filteredIter));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  filteredIter->First();
+
+  for (; !filteredIter->IsDone(); filteredIter->Next()) {
+    if (filteredIter->GetCurrentNode()->NodeType() == nsINode::TEXT_NODE) {
+      // We found a text node! Adjust the document's iterator to point
+      // to the beginning of its text block, then get the current selection.
+      nsresult rv = mFilteredIter->PositionAt(filteredIter->GetCurrentNode());
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      rv = FirstTextNodeInCurrentBlock(mFilteredIter);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      Result<IteratorStatus, nsresult> result =
+          mOffsetTable.Init(*mFilteredIter, IteratorStatus::eValid, mExtent);
+      if (result.isErr()) {
+        NS_WARNING("OffsetEntryArray::Init() failed");
+        mIteratorStatus = IteratorStatus::eValid;  // XXX
+        return result.unwrapErr();
+      }
+      mIteratorStatus = result.unwrap();
+
+      rv = GetSelection(aSelStatus, aSelOffset, aSelLength);
+      NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                           "TextServicesDocument::GetSelection() failed");
+      return rv;
+    }
+  }
+
+  // If we get here, we didn't find any block before or inside
+  // the selection! Just return OK.
+  return NS_OK;
+}
+
+nsresult TextServicesDocument::PrevBlock() {
+  NS_ENSURE_TRUE(mFilteredIter, NS_ERROR_FAILURE);
+
+  if (mIteratorStatus == IteratorStatus::eDone) {
+    return NS_OK;
+  }
+
+  switch (mIteratorStatus) {
+    case IteratorStatus::eValid:
+    case IteratorStatus::eNext: {
+      nsresult rv = FirstTextNodeInPrevBlock(mFilteredIter);
+
+      if (NS_FAILED(rv)) {
+        mIteratorStatus = IteratorStatus::eDone;
+        return rv;
+      }
+
+      if (mFilteredIter->IsDone()) {
+        mIteratorStatus = IteratorStatus::eDone;
+        return NS_OK;
+      }
+
+      mIteratorStatus = IteratorStatus::eValid;
+      break;
+    }
+    case IteratorStatus::ePrev:
+
+      // The iterator already points to the previous
+      // block, so don't do anything.
+
+      mIteratorStatus = IteratorStatus::eValid;
+      break;
+
+    default:
+
+      mIteratorStatus = IteratorStatus::eDone;
+      break;
+  }
+
+  // Keep track of prev and next blocks, just in case
+  // the text service blows away the current block.
+  nsresult rv = NS_OK;
+  if (mIteratorStatus == IteratorStatus::eValid) {
+    GetFirstTextNodeInPrevBlock(getter_AddRefs(mPrevTextBlock));
+    rv = GetFirstTextNodeInNextBlock(getter_AddRefs(mNextTextBlock));
+  } else {
+    // We must be done!
+    mPrevTextBlock = nullptr;
+    mNextTextBlock = nullptr;
+  }
+
+  // XXX The result of GetFirstTextNodeInNextBlock() or NS_OK.
+  return rv;
+}
+
+nsresult TextServicesDocument::NextBlock() {
+  NS_ENSURE_TRUE(mFilteredIter, NS_ERROR_FAILURE);
+
+  if (mIteratorStatus == IteratorStatus::eDone) {
+    return NS_OK;
+  }
+
+  switch (mIteratorStatus) {
+    case IteratorStatus::eValid: {
+      // Advance the iterator to the next text block.
+
+      nsresult rv = FirstTextNodeInNextBlock(mFilteredIter);
+
+      if (NS_FAILED(rv)) {
+        mIteratorStatus = IteratorStatus::eDone;
+        return rv;
+      }
+
+      if (mFilteredIter->IsDone()) {
+        mIteratorStatus = IteratorStatus::eDone;
+        return NS_OK;
+      }
+
+      mIteratorStatus = IteratorStatus::eValid;
+      break;
+    }
+    case IteratorStatus::eNext:
+
+      // The iterator already points to the next block,
+      // so don't do anything to it!
+
+      mIteratorStatus = IteratorStatus::eValid;
+      break;
+
+    case IteratorStatus::ePrev:
+
+      // If the iterator is pointing to the previous block,
+      // we know that there is no next text block! Just
+      // fall through to the default case!
+
+    default:
+
+      mIteratorStatus = IteratorStatus::eDone;
+      break;
+  }
+
+  // Keep track of prev and next blocks, just in case
+  // the text service blows away the current block.
+  nsresult rv = NS_OK;
+  if (mIteratorStatus == IteratorStatus::eValid) {
+    GetFirstTextNodeInPrevBlock(getter_AddRefs(mPrevTextBlock));
+    rv = GetFirstTextNodeInNextBlock(getter_AddRefs(mNextTextBlock));
+  } else {
+    // We must be done.
+    mPrevTextBlock = nullptr;
+    mNextTextBlock = nullptr;
+  }
+
+  // The result of GetFirstTextNodeInNextBlock() or NS_OK.
+  return rv;
+}
+
+nsresult TextServicesDocument::IsDone(bool* aIsDone) {
+  NS_ENSURE_TRUE(aIsDone, NS_ERROR_NULL_POINTER);
+
+  *aIsDone = false;
+
+  NS_ENSURE_TRUE(mFilteredIter, NS_ERROR_FAILURE);
+
+  *aIsDone = mIteratorStatus == IteratorStatus::eDone;
+
+  return NS_OK;
+}
+
+nsresult TextServicesDocument::SetSelection(uint32_t aOffset,
+                                            uint32_t aLength) {
+  NS_ENSURE_TRUE(mSelCon, NS_ERROR_FAILURE);
+
+  return SetSelectionInternal(aOffset, aLength, true);
+}
+
+nsresult TextServicesDocument::ScrollSelectionIntoView() {
+  NS_ENSURE_TRUE(mSelCon, NS_ERROR_FAILURE);
+
+  // After ScrollSelectionIntoView(), the pending notifications might be flushed
+  // and PresShell/PresContext/Frames may be dead. See bug 418470.
+  nsresult rv = mSelCon->ScrollSelectionIntoView(
+      nsISelectionController::SELECTION_NORMAL,
+      nsISelectionController::SELECTION_FOCUS_REGION,
+      nsISelectionController::SCROLL_SYNCHRONOUS);
+
+  return rv;
+}
+
+nsresult TextServicesDocument::OffsetEntryArray::WillDeleteSelection() {
+  MOZ_ASSERT(mSelection.IsSet());
+  MOZ_ASSERT(!mSelection.IsCollapsed());
+
+  for (size_t i = mSelection.StartIndex(); i <= mSelection.EndIndex(); i++) {
+    OffsetEntry* entry = ElementAt(i).get();
+    if (i == mSelection.StartIndex()) {
+      // Calculate the length of the selection. Note that the
+      // selection length can be zero if the start of the selection
+      // is at the very end of a text node entry.
+      uint32_t selLength;
+      if (entry->mIsInsertedText) {
+        // Inserted text offset entries have no width when
+        // talking in terms of string offsets! If the beginning
+        // of the selection is in an inserted text offset entry,
+        // the caret is always at the end of the entry!
+        selLength = 0;
+      } else {
+        selLength = entry->EndOffsetInTextInBlock() -
+                    mSelection.StartOffsetInTextInBlock();
+      }
+
+      if (selLength > 0) {
+        if (mSelection.StartOffsetInTextInBlock() >
+            entry->mOffsetInTextInBlock) {
+          // Selection doesn't start at the beginning of the
+          // text node entry. We need to split this entry into
+          // two pieces, the piece before the selection, and
+          // the piece inside the selection.
+          nsresult rv = SplitElementAt(i, selLength);
+          if (NS_FAILED(rv)) {
+            NS_WARNING("selLength was invalid for the OffsetEntry");
+            return rv;
+          }
+
+          // Adjust selection indexes to account for new entry:
+          MOZ_DIAGNOSTIC_ASSERT(mSelection.StartIndex() + 1 < Length());
+          MOZ_DIAGNOSTIC_ASSERT(mSelection.EndIndex() + 1 < Length());
+          mSelection.SetIndexes(mSelection.StartIndex() + 1,
+                                mSelection.EndIndex() + 1);
+          entry = ElementAt(++i).get();
+        }
+
+        if (mSelection.StartIndex() < mSelection.EndIndex()) {
+          // The entire entry is contained in the selection. Mark the
+          // entry invalid.
+          entry->mIsValid = false;
+        }
+      }
+    }
+
+    if (i == mSelection.EndIndex()) {
+      if (entry->mIsInsertedText) {
+        // Inserted text offset entries have no width when
+        // talking in terms of string offsets! If the end
+        // of the selection is in an inserted text offset entry,
+        // the selection includes the entire entry!
+        entry->mIsValid = false;
+      } else {
+        // Calculate the length of the selection. Note that the
+        // selection length can be zero if the end of the selection
+        // is at the very beginning of a text node entry.
+
+        const uint32_t selLength =
+            mSelection.EndOffsetInTextInBlock() - entry->mOffsetInTextInBlock;
+        if (selLength) {
+          if (mSelection.EndOffsetInTextInBlock() <
+              entry->EndOffsetInTextInBlock()) {
+            // mOffsetInTextInBlock is guaranteed to be inside the selection,
+            // even when mSelection.IsInSameElement() is true.
+            nsresult rv = SplitElementAt(i, entry->mLength - selLength);
+            if (NS_FAILED(rv)) {
+              NS_WARNING(
+                  "entry->mLength - selLength was invalid for the OffsetEntry");
+              return rv;
+            }
+
+            // Update the entry fields:
+            ElementAt(i + 1)->mOffsetInTextNode = entry->mOffsetInTextNode;
+          }
+
+          if (mSelection.EndOffsetInTextInBlock() ==
+              entry->EndOffsetInTextInBlock()) {
+            // The entire entry is contained in the selection. Mark the
+            // entry invalid.
+            entry->mIsValid = false;
+          }
+        }
+      }
+    }
+
+    if (i != mSelection.StartIndex() && i != mSelection.EndIndex()) {
+      // The entire entry is contained in the selection. Mark the
+      // entry invalid.
+      entry->mIsValid = false;
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult TextServicesDocument::DeleteSelection() {
+  if (NS_WARN_IF(!mEditorBase) ||
+      NS_WARN_IF(!mOffsetTable.mSelection.IsSet())) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (mOffsetTable.mSelection.IsCollapsed()) {
+    return NS_OK;
+  }
+
+  // If we have an mExtent, save off its current set of
+  // end points so we can compare them against mExtent's
+  // set after the deletion of the content.
+
+  nsCOMPtr<nsINode> origStartNode, origEndNode;
+  uint32_t origStartOffset = 0, origEndOffset = 0;
+
+  if (mExtent) {
+    nsresult rv = GetRangeEndPoints(
+        mExtent, getter_AddRefs(origStartNode), &origStartOffset,
+        getter_AddRefs(origEndNode), &origEndOffset);
+
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  if (NS_FAILED(mOffsetTable.WillDeleteSelection())) {
+    NS_WARNING(
+        "TextServicesDocument::OffsetEntryTable::WillDeleteSelection() failed");
+    return NS_ERROR_FAILURE;
+  }
+
+  // Make sure mFilteredIter always points to something valid!
+  AdjustContentIterator();
+
+  // Now delete the actual content!
+  OwningNonNull<EditorBase> editorBase = *mEditorBase;
+  nsresult rv = editorBase->DeleteSelectionAsAction(nsIEditor::ePrevious,
+                                                    nsIEditor::eStrip);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Now that we've actually deleted the selected content,
+  // check to see if our mExtent has changed, if so, then
+  // we have to create a new content iterator!
+
+  if (origStartNode && origEndNode) {
+    nsCOMPtr<nsINode> curStartNode, curEndNode;
+    uint32_t curStartOffset = 0, curEndOffset = 0;
+
+    rv = GetRangeEndPoints(mExtent, getter_AddRefs(curStartNode),
+                           &curStartOffset, getter_AddRefs(curEndNode),
+                           &curEndOffset);
+
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    if (origStartNode != curStartNode || origEndNode != curEndNode) {
+      // The range has changed, so we need to create a new content
+      // iterator based on the new range.
+      nsCOMPtr<nsIContent> curContent;
+      if (mIteratorStatus != IteratorStatus::eDone) {
+        // The old iterator is still pointing to something valid,
+        // so get its current node so we can restore it after we
+        // create the new iterator!
+        curContent = mFilteredIter->GetCurrentNode()
+                         ? mFilteredIter->GetCurrentNode()->AsContent()
+                         : nullptr;
+      }
+
+      // Create the new iterator.
+      rv =
+          CreateFilteredContentIterator(mExtent, getter_AddRefs(mFilteredIter));
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      // Now make the new iterator point to the content node
+      // the old one was pointing at.
+      if (curContent) {
+        rv = mFilteredIter->PositionAt(curContent);
+        if (NS_FAILED(rv)) {
+          mIteratorStatus = IteratorStatus::eDone;
+        } else {
+          mIteratorStatus = IteratorStatus::eValid;
+        }
+      }
+    }
+  }
+
+  OffsetEntry* entry = mOffsetTable.DidDeleteSelection();
+  if (entry) {
+    SetSelection(mOffsetTable.mSelection.StartOffsetInTextInBlock(), 0);
+  }
+
+  // Now remove any invalid entries from the offset table.
+  mOffsetTable.RemoveInvalidElements();
+  return NS_OK;
+}
+
+OffsetEntry* TextServicesDocument::OffsetEntryArray::DidDeleteSelection() {
+  MOZ_ASSERT(mSelection.IsSet());
+
+  // Move the caret to the end of the first valid entry.
+  // Start with SelectionStartIndex() since it may still be valid.
+  OffsetEntry* entry = nullptr;
+  for (size_t i = mSelection.StartIndex() + 1; !entry && i > 0; i--) {
+    entry = ElementAt(i - 1).get();
+    if (!entry->mIsValid) {
+      entry = nullptr;
+    } else {
+      MOZ_DIAGNOSTIC_ASSERT(i - 1 < Length());
+      mSelection.Set(i - 1, entry->EndOffsetInTextInBlock());
+    }
+  }
+
+  // If we still don't have a valid entry, move the caret
+  // to the next valid entry after the selection:
+  for (size_t i = mSelection.EndIndex(); !entry && i < Length(); i++) {
+    entry = ElementAt(i).get();
+    if (!entry->mIsValid) {
+      entry = nullptr;
+    } else {
+      MOZ_DIAGNOSTIC_ASSERT(i < Length());
+      mSelection.Set(i, entry->mOffsetInTextInBlock);
+    }
+  }
+
+  if (!entry) {
+    // Uuughh we have no valid offset entry to place our
+    // caret ... just mark the selection invalid.
+    mSelection.Reset();
+  }
+
+  return entry;
+}
+
+nsresult TextServicesDocument::InsertText(const nsAString& aText) {
+  if (NS_WARN_IF(!mEditorBase) ||
+      NS_WARN_IF(!mOffsetTable.mSelection.IsSet())) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // If the selection is not collapsed, we need to save
+  // off the selection offsets so we can restore the
+  // selection and delete the selected content after we've
+  // inserted the new text. This is necessary to try and
+  // retain as much of the original style of the content
+  // being deleted.
+
+  const bool wasSelectionCollapsed = mOffsetTable.mSelection.IsCollapsed();
+  const uint32_t savedSelOffset =
+      mOffsetTable.mSelection.StartOffsetInTextInBlock();
+  const uint32_t savedSelLength = mOffsetTable.mSelection.LengthInTextInBlock();
+
+  if (!wasSelectionCollapsed) {
+    // Collapse to the start of the current selection
+    // for the insert!
+    nsresult rv =
+        SetSelection(mOffsetTable.mSelection.StartOffsetInTextInBlock(), 0);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  // AutoTransactionBatchExternal grabs mEditorBase, so, we don't need to grab
+  // the instance with local variable here.
+  OwningNonNull<EditorBase> editorBase = *mEditorBase;
+  AutoTransactionBatchExternal treatAsOneTransaction(editorBase);
+
+  nsresult rv = editorBase->InsertTextAsAction(aText);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("InsertTextAsAction() failed");
+    return rv;
+  }
+
+  RefPtr<Selection> selection =
+      mSelCon->GetSelection(nsISelectionController::SELECTION_NORMAL);
+  rv = mOffsetTable.DidInsertText(selection, aText);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("TextServicesDocument::OffsetEntry::DidInsertText() failed");
+    return rv;
+  }
+
+  if (!wasSelectionCollapsed) {
+    nsresult rv = SetSelection(savedSelOffset, savedSelLength);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    rv = DeleteSelection();
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult TextServicesDocument::OffsetEntryArray::DidInsertText(
+    dom::Selection* aSelection, const nsAString& aInsertedString) {
+  MOZ_ASSERT(mSelection.IsSet());
+
+  // When you touch this method, please make sure that the entry instance
+  // won't be deleted.  If you know it'll be deleted, you should set it to
+  // `nullptr`.
+  OffsetEntry* entry = ElementAt(mSelection.StartIndex()).get();
+  OwningNonNull<Text> const textNodeAtStartEntry = entry->mTextNode;
+
+  NS_ASSERTION((entry->mIsValid), "Invalid insertion point!");
+
+  if (entry->mOffsetInTextInBlock == mSelection.StartOffsetInTextInBlock()) {
+    if (entry->mIsInsertedText) {
+      // If the caret is in an inserted text offset entry,
+      // we simply insert the text at the end of the entry.
+      entry->mLength += aInsertedString.Length();
+    } else {
+      // Insert an inserted text offset entry before the current
+      // entry!
+      UniquePtr<OffsetEntry> newInsertedTextEntry =
+          MakeUnique<OffsetEntry>(entry->mTextNode, entry->mOffsetInTextInBlock,
+                                  aInsertedString.Length());
+      newInsertedTextEntry->mIsInsertedText = true;
+      newInsertedTextEntry->mOffsetInTextNode = entry->mOffsetInTextNode;
+      // XXX(Bug 1631371) Check if this should use a fallible operation as it
+      // pretended earlier.
+      InsertElementAt(mSelection.StartIndex(), std::move(newInsertedTextEntry));
+    }
+  } else if (entry->EndOffsetInTextInBlock() ==
+             mSelection.EndOffsetInTextInBlock()) {
+    // We are inserting text at the end of the current offset entry.
+    // Look at the next valid entry in the table. If it's an inserted
+    // text entry, add to its length and adjust its node offset. If
+    // it isn't, add a new inserted text entry.
+    uint32_t nextIndex = mSelection.StartIndex() + 1;
+    OffsetEntry* insertedTextEntry = nullptr;
+    if (Length() > nextIndex) {
+      insertedTextEntry = ElementAt(nextIndex).get();
+      if (!insertedTextEntry) {
+        return NS_ERROR_FAILURE;
+      }
+
+      // Check if the entry is a match. If it isn't, set
+      // iEntry to zero.
+      if (!insertedTextEntry->mIsInsertedText ||
+          insertedTextEntry->mOffsetInTextInBlock !=
+              mSelection.StartOffsetInTextInBlock()) {
+        insertedTextEntry = nullptr;
+      }
+    }
+
+    if (!insertedTextEntry) {
+      // We didn't find an inserted text offset entry, so
+      // create one.
+      UniquePtr<OffsetEntry> newInsertedTextEntry = MakeUnique<OffsetEntry>(
+          entry->mTextNode, mSelection.StartOffsetInTextInBlock(), 0);
+      newInsertedTextEntry->mOffsetInTextNode = entry->EndOffsetInTextNode();
+      newInsertedTextEntry->mIsInsertedText = true;
+      // XXX(Bug 1631371) Check if this should use a fallible operation as it
+      // pretended earlier.
+      insertedTextEntry =
+          InsertElementAt(nextIndex, std::move(newInsertedTextEntry))->get();
+    }
+
+    // We have a valid inserted text offset entry. Update its
+    // length, adjust the selection indexes, and make sure the
+    // caret is properly placed!
+
+    insertedTextEntry->mLength += aInsertedString.Length();
+
+    MOZ_DIAGNOSTIC_ASSERT(nextIndex < Length());
+    mSelection.SetIndex(nextIndex);
+
+    if (!aSelection) {
+      return NS_OK;
+    }
+
+    OwningNonNull<Text> textNode = insertedTextEntry->mTextNode;
+    nsresult rv = aSelection->CollapseInLimiter(
+        textNode, insertedTextEntry->EndOffsetInTextNode());
+    if (NS_FAILED(rv)) {
+      NS_WARNING("Selection::CollapseInLimiter() failed");
+      return rv;
+    }
+  } else if (entry->EndOffsetInTextInBlock() >
+             mSelection.StartOffsetInTextInBlock()) {
+    // We are inserting text into the middle of the current offset entry.
+    // split the current entry into two parts, then insert an inserted text
+    // entry between them!
+    nsresult rv = SplitElementAt(mSelection.StartIndex(),
+                                 entry->EndOffsetInTextInBlock() -
+                                     mSelection.StartOffsetInTextInBlock());
+    if (NS_FAILED(rv)) {
+      NS_WARNING(
+          "entry->EndOffsetInTextInBlock() - "
+          "mSelection.StartOffsetInTextInBlock() was invalid for the "
+          "OffsetEntry");
+      return rv;
+    }
+
+    // XXX(Bug 1631371) Check if this should use a fallible operation as it
+    // pretended earlier.
+    UniquePtr<OffsetEntry>& insertedTextEntry = *InsertElementAt(
+        mSelection.StartIndex() + 1,
+        MakeUnique<OffsetEntry>(entry->mTextNode,
+                                mSelection.StartOffsetInTextInBlock(),
+                                aInsertedString.Length()));
+    LockOffsetEntryArrayLengthInDebugBuild(observer, *this);
+    insertedTextEntry->mIsInsertedText = true;
+    insertedTextEntry->mOffsetInTextNode = entry->EndOffsetInTextNode();
+    MOZ_DIAGNOSTIC_ASSERT(mSelection.StartIndex() + 1 < Length());
+    mSelection.SetIndex(mSelection.StartIndex() + 1);
+  }
+
+  // We've just finished inserting an inserted text offset entry.
+  // update all entries with the same mTextNode pointer that follow
+  // it in the table!
+
+  for (size_t i = mSelection.StartIndex() + 1; i < Length(); i++) {
+    const UniquePtr<OffsetEntry>& entry = ElementAt(i);
+    LockOffsetEntryArrayLengthInDebugBuild(observer, *this);
+    if (entry->mTextNode != textNodeAtStartEntry) {
+      break;
+    }
+    if (entry->mIsValid) {
+      entry->mOffsetInTextNode += aInsertedString.Length();
+    }
+  }
+
+  return NS_OK;
+}
+
+void TextServicesDocument::DidDeleteContent(const nsIContent& aChildContent) {
+  if (NS_WARN_IF(!mFilteredIter) || !aChildContent.IsText()) {
+    return;
+  }
+
+  Maybe<size_t> maybeNodeIndex =
+      mOffsetTable.FirstIndexOf(*aChildContent.AsText());
+  if (maybeNodeIndex.isNothing()) {
+    // It's okay if the node isn't in the offset table, the
+    // editor could be cleaning house.
+    return;
+  }
+
+  nsINode* node = mFilteredIter->GetCurrentNode();
+  if (node && node == &aChildContent &&
+      mIteratorStatus != IteratorStatus::eDone) {
+    // XXX: This should never really happen because
+    // AdjustContentIterator() should have been called prior
+    // to the delete to try and position the iterator on the
+    // next valid text node in the offset table, and if there
+    // wasn't a next, it would've set mIteratorStatus to eIsDone.
+
+    NS_ERROR("DeleteNode called for current iterator node.");
+  }
+
+  for (size_t nodeIndex = *maybeNodeIndex; nodeIndex < mOffsetTable.Length();
+       nodeIndex++) {
+    const UniquePtr<OffsetEntry>& entry = mOffsetTable[nodeIndex];
+    LockOffsetEntryArrayLengthInDebugBuild(observer, mOffsetTable);
+    if (!entry) {
+      return;
+    }
+
+    if (entry->mTextNode == &aChildContent) {
+      entry->mIsValid = false;
+    }
+  }
+}
+
+void TextServicesDocument::DidJoinContents(
+    const EditorRawDOMPoint& aJoinedPoint, const nsIContent& aRemovedContent) {
+  // Make sure that both nodes are text nodes -- otherwise we don't care.
+  if (!aJoinedPoint.IsInTextNode() || !aRemovedContent.IsText()) {
+    return;
+  }
+
+  // Note: The editor merges the contents of the left node into the
+  //       contents of the right.
+
+  Maybe<size_t> maybeRemovedIndex =
+      mOffsetTable.FirstIndexOf(*aRemovedContent.AsText());
+  if (maybeRemovedIndex.isNothing()) {
+    // It's okay if the node isn't in the offset table, the
+    // editor could be cleaning house.
+    return;
+  }
+
+  Maybe<size_t> maybeJoinedIndex =
+      mOffsetTable.FirstIndexOf(*aJoinedPoint.ContainerAs<Text>());
+  if (maybeJoinedIndex.isNothing()) {
+    // It's okay if the node isn't in the offset table, the
+    // editor could be cleaning house.
+    return;
+  }
+
+  const size_t removedIndex = *maybeRemovedIndex;
+  const size_t joinedIndex = *maybeJoinedIndex;
+
+  if (MOZ_UNLIKELY(joinedIndex > removedIndex)) {
+    NS_ASSERTION(joinedIndex < removedIndex, "Indexes out of order.");
+    return;
+  }
+  NS_ASSERTION(mOffsetTable[removedIndex]->mOffsetInTextNode == 0,
+               "Unexpected offset value for rightIndex.");
+
+  // Run through the table and change all entries referring to
+  // the removed node so that they now refer to the joined node,
+  // and adjust offsets if necessary.
+  const uint32_t movedTextDataLength =
+      aJoinedPoint.ContainerAs<Text>()->TextDataLength() -
+      aJoinedPoint.Offset();
+  for (uint32_t i = removedIndex; i < mOffsetTable.Length(); i++) {
+    const UniquePtr<OffsetEntry>& entry = mOffsetTable[i];
+    LockOffsetEntryArrayLengthInDebugBuild(observer, mOffsetTable);
+    if (entry->mTextNode != aRemovedContent.AsText()) {
+      break;
+    }
+    if (entry->mIsValid) {
+      entry->mTextNode = aJoinedPoint.ContainerAs<Text>();
+      // The text was moved from aRemovedContent to end of the container of
+      // aJoinedPoint.
+      entry->mOffsetInTextNode += movedTextDataLength;
+    }
+  }
+
+  // Now check to see if the iterator is pointing to the
+  // left node. If it is, make it point to the joined node!
+  if (mFilteredIter->GetCurrentNode() == aRemovedContent.AsText()) {
+    mFilteredIter->PositionAt(aJoinedPoint.ContainerAs<Text>());
+  }
+}
+
+nsresult TextServicesDocument::CreateFilteredContentIterator(
+    const AbstractRange* aAbstractRange,
+    FilteredContentIterator** aFilteredIter) {
+  if (NS_WARN_IF(!aAbstractRange) || NS_WARN_IF(!aFilteredIter)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  *aFilteredIter = nullptr;
+
+  UniquePtr<nsComposeTxtSrvFilter> composeFilter;
+  switch (mTxtSvcFilterType) {
+    case nsIEditorSpellCheck::FILTERTYPE_NORMAL:
+      composeFilter = nsComposeTxtSrvFilter::CreateNormalFilter();
+      break;
+    case nsIEditorSpellCheck::FILTERTYPE_MAIL:
+      composeFilter = nsComposeTxtSrvFilter::CreateMailFilter();
+      break;
+  }
+
+  // Create a FilteredContentIterator
+  // This class wraps the ContentIterator in order to give itself a chance
+  // to filter out certain content nodes
+  RefPtr<FilteredContentIterator> filter =
+      new FilteredContentIterator(std::move(composeFilter));
+  nsresult rv = filter->Init(aAbstractRange);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  filter.forget(aFilteredIter);
+  return NS_OK;
+}
+
+Element* TextServicesDocument::GetDocumentContentRootNode() const {
+  if (NS_WARN_IF(!mDocument)) {
+    return nullptr;
+  }
+
+  if (mDocument->IsHTMLOrXHTML()) {
+    Element* rootElement = mDocument->GetRootElement();
+    if (rootElement && rootElement->IsXULElement()) {
+      // HTML documents with root XUL elements should eventually be transitioned
+      // to a regular document structure, but for now the content root node will
+      // be the document element.
+      return mDocument->GetDocumentElement();
+    }
+    // For HTML documents, the content root node is the body.
+    return mDocument->GetBody();
+  }
+
+  // For non-HTML documents, the content root node will be the document element.
+  return mDocument->GetDocumentElement();
+}
+
+already_AddRefed<nsRange> TextServicesDocument::CreateDocumentContentRange() {
+  nsCOMPtr<nsINode> node = GetDocumentContentRootNode();
+  if (NS_WARN_IF(!node)) {
+    return nullptr;
+  }
+
+  RefPtr<nsRange> range = nsRange::Create(node);
+  IgnoredErrorResult ignoredError;
+  range->SelectNodeContents(*node, ignoredError);
+  NS_WARNING_ASSERTION(!ignoredError.Failed(), "SelectNodeContents() failed");
+  return range.forget();
+}
+
+already_AddRefed<nsRange>
+TextServicesDocument::CreateDocumentContentRootToNodeOffsetRange(
+    nsINode* aParent, uint32_t aOffset, bool aToStart) {
+  if (NS_WARN_IF(!aParent)) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsINode> bodyNode = GetDocumentContentRootNode();
+  if (NS_WARN_IF(!bodyNode)) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsINode> startNode;
+  nsCOMPtr<nsINode> endNode;
+  uint32_t startOffset, endOffset;
+
+  if (aToStart) {
+    // The range should begin at the start of the document
+    // and extend up until (aParent, aOffset).
+    startNode = bodyNode;
+    startOffset = 0;
+    endNode = aParent;
+    endOffset = aOffset;
+  } else {
+    // The range should begin at (aParent, aOffset) and
+    // extend to the end of the document.
+    startNode = aParent;
+    startOffset = aOffset;
+    endNode = bodyNode;
+    endOffset = endNode ? endNode->GetChildCount() : 0;
+  }
+
+  RefPtr<nsRange> range = nsRange::Create(startNode, startOffset, endNode,
+                                          endOffset, IgnoreErrors());
+  NS_WARNING_ASSERTION(range,
+                       "nsRange::Create() failed to create new valid range");
+  return range.forget();
+}
+
+nsresult TextServicesDocument::CreateDocumentContentIterator(
+    FilteredContentIterator** aFilteredIter) {
+  NS_ENSURE_TRUE(aFilteredIter, NS_ERROR_NULL_POINTER);
+
+  RefPtr<nsRange> range = CreateDocumentContentRange();
+  if (NS_WARN_IF(!range)) {
+    *aFilteredIter = nullptr;
+    return NS_ERROR_FAILURE;
+  }
+
+  return CreateFilteredContentIterator(range, aFilteredIter);
+}
+
+nsresult TextServicesDocument::AdjustContentIterator() {
+  NS_ENSURE_TRUE(mFilteredIter, NS_ERROR_FAILURE);
+
+  nsCOMPtr<nsINode> node = mFilteredIter->GetCurrentNode();
+  NS_ENSURE_TRUE(node, NS_ERROR_FAILURE);
+
+  Text* prevValidTextNode = nullptr;
+  Text* nextValidTextNode = nullptr;
+  bool foundEntry = false;
+
+  const size_t tableLength = mOffsetTable.Length();
+  for (size_t i = 0; i < tableLength && !nextValidTextNode; i++) {
+    UniquePtr<OffsetEntry>& entry = mOffsetTable[i];
+    LockOffsetEntryArrayLengthInDebugBuild(observer, mOffsetTable);
+    if (entry->mTextNode == node) {
+      if (entry->mIsValid) {
+        // The iterator is still pointing to something valid!
+        // Do nothing!
+        return NS_OK;
+      }
+      // We found an invalid entry that points to
+      // the current iterator node. Stop looking for
+      // a previous valid node!
+      foundEntry = true;
+    }
+
+    if (entry->mIsValid) {
+      if (!foundEntry) {
+        prevValidTextNode = entry->mTextNode;
+      } else {
+        nextValidTextNode = entry->mTextNode;
+      }
+    }
+  }
+
+  Text* validTextNode = nullptr;
+  if (prevValidTextNode) {
+    validTextNode = prevValidTextNode;
+  } else if (nextValidTextNode) {
+    validTextNode = nextValidTextNode;
+  }
+
+  if (validTextNode) {
+    nsresult rv = mFilteredIter->PositionAt(validTextNode);
+    if (NS_FAILED(rv)) {
+      mIteratorStatus = IteratorStatus::eDone;
+    } else {
+      mIteratorStatus = IteratorStatus::eValid;
+    }
+    return rv;
+  }
+
+  // If we get here, there aren't any valid entries
+  // in the offset table! Try to position the iterator
+  // on the next text block first, then previous if
+  // one doesn't exist!
+
+  if (mNextTextBlock) {
+    nsresult rv = mFilteredIter->PositionAt(mNextTextBlock);
+    if (NS_FAILED(rv)) {
+      mIteratorStatus = IteratorStatus::eDone;
+      return rv;
+    }
+
+    mIteratorStatus = IteratorStatus::eNext;
+  } else if (mPrevTextBlock) {
+    nsresult rv = mFilteredIter->PositionAt(mPrevTextBlock);
+    if (NS_FAILED(rv)) {
+      mIteratorStatus = IteratorStatus::eDone;
+      return rv;
+    }
+
+    mIteratorStatus = IteratorStatus::ePrev;
+  } else {
+    mIteratorStatus = IteratorStatus::eDone;
+  }
+  return NS_OK;
+}
+
+// static
+bool TextServicesDocument::DidSkip(FilteredContentIterator* aFilteredIter) {
+  return aFilteredIter && aFilteredIter->DidSkip();
+}
+
+// static
+void TextServicesDocument::ClearDidSkip(
+    FilteredContentIterator* aFilteredIter) {
+  // Clear filter's skip flag
+  if (aFilteredIter) {
+    aFilteredIter->ClearDidSkip();
+  }
+}
+
+// static
+bool TextServicesDocument::HasSameBlockNodeParent(Text& aTextNode1,
+                                                  Text& aTextNode2) {
+  // XXX How about the case that both text nodes are orphan nodes?
+  if (aTextNode1.GetParent() == aTextNode2.GetParent()) {
+    return true;
+  }
+
+  // I think that spellcheck should be available only in editable nodes.
+  // So, we also need to check whether they are in same editing host.
+  const Element* editableBlockElementOrInlineEditingHost1 =
+      HTMLEditUtils::GetAncestorElement(
+          aTextNode1,
+          HTMLEditUtils::ClosestEditableBlockElementOrInlineEditingHost,
+          BlockInlineCheck::UseHTMLDefaultStyle);
+  const Element* editableBlockElementOrInlineEditingHost2 =
+      HTMLEditUtils::GetAncestorElement(
+          aTextNode2,
+          HTMLEditUtils::ClosestEditableBlockElementOrInlineEditingHost,
+          BlockInlineCheck::UseHTMLDefaultStyle);
+  return editableBlockElementOrInlineEditingHost1 &&
+         editableBlockElementOrInlineEditingHost1 ==
+             editableBlockElementOrInlineEditingHost2;
+}
+
+Result<EditorRawDOMRangeInTexts, nsresult>
+TextServicesDocument::OffsetEntryArray::WillSetSelection(
+    uint32_t aOffsetInTextInBlock, uint32_t aLength) {
+  // Find start of selection in node offset terms:
+  EditorRawDOMPointInText newStart;
+  for (size_t i = 0; !newStart.IsSet() && i < Length(); i++) {
+    const UniquePtr<OffsetEntry>& entry = ElementAt(i);
+    LockOffsetEntryArrayLengthInDebugBuild(observer, *this);
+    if (entry->mIsValid) {
+      if (entry->mIsInsertedText) {
+        // Caret can only be placed at the end of an
+        // inserted text offset entry, if the offsets
+        // match exactly!
+        if (entry->mOffsetInTextInBlock == aOffsetInTextInBlock) {
+          newStart.Set(entry->mTextNode, entry->EndOffsetInTextNode());
+        }
+      } else if (aOffsetInTextInBlock >= entry->mOffsetInTextInBlock) {
+        bool foundEntry = false;
+        if (aOffsetInTextInBlock < entry->EndOffsetInTextInBlock()) {
+          foundEntry = true;
+        } else if (aOffsetInTextInBlock == entry->EndOffsetInTextInBlock()) {
+          // Peek after this entry to see if we have any
+          // inserted text entries belonging to the same
+          // entry->mTextNode. If so, we have to place the selection
+          // after it!
+          if (i + 1 < Length()) {
+            const UniquePtr<OffsetEntry>& nextEntry = ElementAt(i + 1);
+            LockOffsetEntryArrayLengthInDebugBuild(observer, *this);
+            if (!nextEntry->mIsValid ||
+                nextEntry->mOffsetInTextInBlock != aOffsetInTextInBlock) {
+              // Next offset entry isn't an exact match, so we'll
+              // just use the current entry.
+              foundEntry = true;
+            }
+          }
+        }
+
+        if (foundEntry) {
+          newStart.Set(entry->mTextNode, entry->mOffsetInTextNode +
+                                             aOffsetInTextInBlock -
+                                             entry->mOffsetInTextInBlock);
+        }
+      }
+
+      if (newStart.IsSet()) {
+        MOZ_DIAGNOSTIC_ASSERT(i < Length());
+        mSelection.Set(i, aOffsetInTextInBlock);
+      }
+    }
+  }
+
+  if (NS_WARN_IF(!newStart.IsSet())) {
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  if (!aLength) {
+    mSelection.CollapseToStart();
+    return EditorRawDOMRangeInTexts(newStart);
+  }
+
+  // Find the end of the selection in node offset terms:
+  EditorRawDOMPointInText newEnd;
+  const uint32_t endOffset = aOffsetInTextInBlock + aLength;
+  for (uint32_t i = Length(); !newEnd.IsSet() && i > 0; i--) {
+    const UniquePtr<OffsetEntry>& entry = ElementAt(i - 1);
+    LockOffsetEntryArrayLengthInDebugBuild(observer, *this);
+    if (entry->mIsValid) {
+      if (entry->mIsInsertedText) {
+        if (entry->mOffsetInTextInBlock ==
+            (newEnd.IsSet() ? newEnd.Offset() : 0)) {
+          // If the selection ends on an inserted text offset entry,
+          // the selection includes the entire entry!
+          newEnd.Set(entry->mTextNode, entry->EndOffsetInTextNode());
+        }
+      } else if (entry->OffsetInTextInBlockIsInRangeOrEndOffset(endOffset)) {
+        newEnd.Set(entry->mTextNode, entry->mOffsetInTextNode + endOffset -
+                                         entry->mOffsetInTextInBlock);
+      }
+
+      if (newEnd.IsSet()) {
+        MOZ_DIAGNOSTIC_ASSERT(mSelection.StartIndex() < Length());
+        MOZ_DIAGNOSTIC_ASSERT(i - 1 < Length());
+        mSelection.Set(mSelection.StartIndex(), i - 1,
+                       mSelection.StartOffsetInTextInBlock(), endOffset);
+      }
+    }
+  }
+
+  return newEnd.IsSet() ? EditorRawDOMRangeInTexts(newStart, newEnd)
+                        : EditorRawDOMRangeInTexts(newStart);
+}
+
+nsresult TextServicesDocument::SetSelectionInternal(
+    uint32_t aOffsetInTextInBlock, uint32_t aLength, bool aDoUpdate) {
+  if (NS_WARN_IF(!mSelCon)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  Result<EditorRawDOMRangeInTexts, nsresult> newSelectionRange =
+      mOffsetTable.WillSetSelection(aOffsetInTextInBlock, aLength);
+  if (newSelectionRange.isErr()) {
+    NS_WARNING(
+        "TextServicesDocument::OffsetEntryArray::WillSetSelection() failed");
+    return newSelectionRange.unwrapErr();
+  }
+
+  if (!aDoUpdate) {
+    return NS_OK;
+  }
+
+  // XXX: If we ever get a SetSelection() method in nsIEditor, we should
+  //      use it.
+  RefPtr<Selection> selection =
+      mSelCon->GetSelection(nsISelectionController::SELECTION_NORMAL);
+  if (NS_WARN_IF(!selection)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (newSelectionRange.inspect().Collapsed()) {
+    nsresult rv =
+        selection->CollapseInLimiter(newSelectionRange.inspect().StartRef());
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                         "Selection::CollapseInLimiter() failed");
+    return rv;
+  }
+
+  ErrorResult error;
+  selection->SetStartAndEndInLimiter(newSelectionRange.inspect().StartRef(),
+                                     newSelectionRange.inspect().EndRef(),
+                                     error);
+  NS_WARNING_ASSERTION(!error.Failed(),
+                       "Selection::SetStartAndEndInLimiter() failed");
+  return error.StealNSResult();
+}
+
+nsresult TextServicesDocument::GetSelection(BlockSelectionStatus* aSelStatus,
+                                            uint32_t* aSelOffset,
+                                            uint32_t* aSelLength) {
+  NS_ENSURE_TRUE(aSelStatus && aSelOffset && aSelLength, NS_ERROR_NULL_POINTER);
+
+  *aSelStatus = BlockSelectionStatus::eBlockNotFound;
+  *aSelOffset = UINT32_MAX;
+  *aSelLength = UINT32_MAX;
+
+  NS_ENSURE_TRUE(mDocument && mSelCon, NS_ERROR_FAILURE);
+
+  if (mIteratorStatus == IteratorStatus::eDone) {
+    return NS_OK;
+  }
+
+  RefPtr<Selection> selection =
+      mSelCon->GetSelection(nsISelectionController::SELECTION_NORMAL);
+  NS_ENSURE_TRUE(selection, NS_ERROR_FAILURE);
+
+  if (selection->IsCollapsed()) {
+    return GetCollapsedSelection(aSelStatus, aSelOffset, aSelLength);
+  }
+
+  return GetUncollapsedSelection(aSelStatus, aSelOffset, aSelLength);
+}
+
+nsresult TextServicesDocument::GetCollapsedSelection(
+    BlockSelectionStatus* aSelStatus, uint32_t* aSelOffset,
+    uint32_t* aSelLength) {
+  RefPtr<Selection> selection =
+      mSelCon->GetSelection(nsISelectionController::SELECTION_NORMAL);
+  NS_ENSURE_TRUE(selection, NS_ERROR_FAILURE);
+
+  // The calling function should have done the GetIsCollapsed()
+  // check already. Just assume it's collapsed!
+  *aSelStatus = BlockSelectionStatus::eBlockOutside;
+  *aSelOffset = *aSelLength = UINT32_MAX;
+
+  const uint32_t tableCount = mOffsetTable.Length();
+  if (!tableCount) {
+    return NS_OK;
+  }
+
+  // Get pointers to the first and last offset entries
+  // in the table.
+
+  UniquePtr<OffsetEntry>& eStart = mOffsetTable[0];
+  UniquePtr<OffsetEntry>& eEnd =
+      tableCount > 1 ? mOffsetTable[tableCount - 1] : eStart;
+  LockOffsetEntryArrayLengthInDebugBuild(observer, mOffsetTable);
+
+  const uint32_t eStartOffset = eStart->mOffsetInTextNode;
+  const uint32_t eEndOffset = eEnd->EndOffsetInTextNode();
+
+  RefPtr<const nsRange> range = selection->GetRangeAt(0);
+  NS_ENSURE_STATE(range);
+
+  nsCOMPtr<nsINode> parent = range->GetStartContainer();
+  MOZ_ASSERT(parent);
+
+  uint32_t offset = range->StartOffset();
+
+  const Maybe<int32_t> e1s1 = nsContentUtils::ComparePoints(
+      eStart->mTextNode, eStartOffset, parent, offset);
+  const Maybe<int32_t> e2s1 = nsContentUtils::ComparePoints(
+      eEnd->mTextNode, eEndOffset, parent, offset);
+
+  if (MOZ_UNLIKELY(NS_WARN_IF(!e1s1) || NS_WARN_IF(!e2s1))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (*e1s1 > 0 || *e2s1 < 0) {
+    // We're done if the caret is outside the current text block.
+    return NS_OK;
+  }
+
+  if (parent->IsText()) {
+    // Good news, the caret is in a text node. Look
+    // through the offset table for the entry that
+    // matches its parent and offset.
+
+    for (uint32_t i = 0; i < tableCount; i++) {
+      const UniquePtr<OffsetEntry>& entry = mOffsetTable[i];
+      LockOffsetEntryArrayLengthInDebugBuild(observer, mOffsetTable);
+      if (entry->mTextNode == parent->AsText() &&
+          entry->OffsetInTextNodeIsInRangeOrEndOffset(offset)) {
+        *aSelStatus = BlockSelectionStatus::eBlockContains;
+        *aSelOffset =
+            entry->mOffsetInTextInBlock + (offset - entry->mOffsetInTextNode);
+        *aSelLength = 0;
+        return NS_OK;
+      }
+    }
+
+    // If we get here, we didn't find a text node entry
+    // in our offset table that matched.
+    return NS_ERROR_FAILURE;
+  }
+
+  // The caret is in our text block, but it's positioned in some
+  // non-text node (ex. <b>). Create a range based on the start
+  // and end of the text block, then create an iterator based on
+  // this range, with its initial position set to the closest
+  // child of this non-text node. Then look for the closest text
+  // node.
+
+  range = nsRange::Create(eStart->mTextNode, eStartOffset, eEnd->mTextNode,
+                          eEndOffset, IgnoreErrors());
+  if (NS_WARN_IF(!range)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<FilteredContentIterator> filteredIter;
+  nsresult rv =
+      CreateFilteredContentIterator(range, getter_AddRefs(filteredIter));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsIContent* saveNode;
+  if (parent->HasChildren()) {
+    // XXX: We need to make sure that all of parent's
+    //      children are in the text block.
+
+    // If the parent has children, position the iterator
+    // on the child that is to the left of the offset.
+
+    nsIContent* content = range->GetChildAtStartOffset();
+    if (content && parent->GetFirstChild() != content) {
+      content = content->GetPreviousSibling();
+    }
+    NS_ENSURE_TRUE(content, NS_ERROR_FAILURE);
+
+    nsresult rv = filteredIter->PositionAt(content);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    saveNode = content;
+  } else {
+    // The parent has no children, so position the iterator
+    // on the parent.
+    NS_ENSURE_TRUE(parent->IsContent(), NS_ERROR_FAILURE);
+    nsCOMPtr<nsIContent> content = parent->AsContent();
+
+    nsresult rv = filteredIter->PositionAt(content);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    saveNode = content;
+  }
+
+  // Now iterate to the left, towards the beginning of
+  // the text block, to find the first text node you
+  // come across.
+
+  Text* textNode = nullptr;
+  for (; !filteredIter->IsDone(); filteredIter->Prev()) {
+    nsINode* current = filteredIter->GetCurrentNode();
+    if (current->IsText()) {
+      textNode = current->AsText();
+      break;
+    }
+  }
+
+  if (textNode) {
+    // We found a node, now set the offset to the end
+    // of the text node.
+    offset = textNode->TextLength();
+  } else {
+    // We should never really get here, but I'm paranoid.
+
+    // We didn't find a text node above, so iterate to
+    // the right, towards the end of the text block, looking
+    // for a text node.
+
+    nsresult rv = filteredIter->PositionAt(saveNode);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    textNode = nullptr;
+    for (; !filteredIter->IsDone(); filteredIter->Next()) {
+      nsINode* current = filteredIter->GetCurrentNode();
+      if (current->IsText()) {
+        textNode = current->AsText();
+        break;
+      }
+    }
+    NS_ENSURE_TRUE(textNode, NS_ERROR_FAILURE);
+
+    // We found a text node, so set the offset to
+    // the beginning of the node.
+    offset = 0;
+  }
+
+  for (size_t i = 0; i < tableCount; i++) {
+    const UniquePtr<OffsetEntry>& entry = mOffsetTable[i];
+    LockOffsetEntryArrayLengthInDebugBuild(observer, mOffsetTable);
+    if (entry->mTextNode == textNode &&
+        entry->OffsetInTextNodeIsInRangeOrEndOffset(offset)) {
+      *aSelStatus = BlockSelectionStatus::eBlockContains;
+      *aSelOffset =
+          entry->mOffsetInTextInBlock + (offset - entry->mOffsetInTextNode);
+      *aSelLength = 0;
+
+      // Now move the caret so that it is actually in the text node.
+      // We do this to keep things in sync.
+      //
+      // In most cases, the user shouldn't see any movement in the caret
+      // on screen.
+      return SetSelectionInternal(*aSelOffset, *aSelLength, true);
+    }
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+nsresult TextServicesDocument::GetUncollapsedSelection(
+    BlockSelectionStatus* aSelStatus, uint32_t* aSelOffset,
+    uint32_t* aSelLength) {
+  RefPtr<const nsRange> range;
+  RefPtr<Selection> selection =
+      mSelCon->GetSelection(nsISelectionController::SELECTION_NORMAL);
+  NS_ENSURE_TRUE(selection, NS_ERROR_FAILURE);
+
+  // It is assumed that the calling function has made sure that the
+  // selection is not collapsed, and that the input params to this
+  // method are initialized to some defaults.
+
+  nsCOMPtr<nsINode> startContainer, endContainer;
+
+  const size_t tableCount = mOffsetTable.Length();
+
+  // Get pointers to the first and last offset entries
+  // in the table.
+
+  UniquePtr<OffsetEntry>& eStart = mOffsetTable[0];
+  UniquePtr<OffsetEntry>& eEnd =
+      tableCount > 1 ? mOffsetTable[tableCount - 1] : eStart;
+  LockOffsetEntryArrayLengthInDebugBuild(observer, mOffsetTable);
+
+  const uint32_t eStartOffset = eStart->mOffsetInTextNode;
+  const uint32_t eEndOffset = eEnd->EndOffsetInTextNode();
+
+  const uint32_t rangeCount = selection->RangeCount();
+  MOZ_ASSERT(rangeCount);
+
+  // Find the first range in the selection that intersects
+  // the current text block.
+  Maybe<int32_t> e1s2;
+  Maybe<int32_t> e2s1;
+  uint32_t startOffset, endOffset;
+  for (const uint32_t i : IntegerRange(rangeCount)) {
+    MOZ_ASSERT(selection->RangeCount() == rangeCount);
+    range = selection->GetRangeAt(i);
+    if (MOZ_UNLIKELY(NS_WARN_IF(!range))) {
+      return NS_ERROR_FAILURE;
+    }
+
+    nsresult rv =
+        GetRangeEndPoints(range, getter_AddRefs(startContainer), &startOffset,
+                          getter_AddRefs(endContainer), &endOffset);
+
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    e1s2 = nsContentUtils::ComparePoints(eStart->mTextNode, eStartOffset,
+                                         endContainer, endOffset);
+    if (NS_WARN_IF(!e1s2)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    e2s1 = nsContentUtils::ComparePoints(eEnd->mTextNode, eEndOffset,
+                                         startContainer, startOffset);
+    if (NS_WARN_IF(!e2s1)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    // Break out of the loop if the text block intersects the current range.
+
+    if (*e1s2 <= 0 && *e2s1 >= 0) {
+      break;
+    }
+  }
+
+  // We're done if we didn't find an intersecting range.
+
+  if (rangeCount < 1 || *e1s2 > 0 || *e2s1 < 0) {
+    *aSelStatus = BlockSelectionStatus::eBlockOutside;
+    *aSelOffset = *aSelLength = UINT32_MAX;
+    return NS_OK;
+  }
+
+  // Now that we have an intersecting range, find out more info:
+  const Maybe<int32_t> e1s1 = nsContentUtils::ComparePoints(
+      eStart->mTextNode, eStartOffset, startContainer, startOffset);
+  if (NS_WARN_IF(!e1s1)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  const Maybe<int32_t> e2s2 = nsContentUtils::ComparePoints(
+      eEnd->mTextNode, eEndOffset, endContainer, endOffset);
+  if (NS_WARN_IF(!e2s2)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (rangeCount > 1) {
+    // There are multiple selection ranges, we only deal
+    // with the first one that intersects the current,
+    // text block, so mark this a as a partial.
+    *aSelStatus = BlockSelectionStatus::eBlockPartial;
+  } else if (*e1s1 > 0 && *e2s2 < 0) {
+    // The range extends beyond the start and
+    // end of the current text block.
+    *aSelStatus = BlockSelectionStatus::eBlockInside;
+  } else if (*e1s1 <= 0 && *e2s2 >= 0) {
+    // The current text block contains the entire
+    // range.
+    *aSelStatus = BlockSelectionStatus::eBlockContains;
+  } else {
+    // The range partially intersects the block.
+    *aSelStatus = BlockSelectionStatus::eBlockPartial;
+  }
+
+  // Now create a range based on the intersection of the
+  // text block and range:
+
+  nsCOMPtr<nsINode> p1, p2;
+  uint32_t o1, o2;
+
+  // The start of the range will be the rightmost
+  // start node.
+
+  if (*e1s1 >= 0) {
+    p1 = eStart->mTextNode;
+    o1 = eStartOffset;
+  } else {
+    p1 = startContainer;
+    o1 = startOffset;
+  }
+
+  // The end of the range will be the leftmost
+  // end node.
+
+  if (*e2s2 <= 0) {
+    p2 = eEnd->mTextNode;
+    o2 = eEndOffset;
+  } else {
+    p2 = endContainer;
+    o2 = endOffset;
+  }
+
+  range = nsRange::Create(p1, o1, p2, o2, IgnoreErrors());
+  if (NS_WARN_IF(!range)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Now iterate over this range to figure out the selection's
+  // block offset and length.
+
+  RefPtr<FilteredContentIterator> filteredIter;
+  nsresult rv =
+      CreateFilteredContentIterator(range, getter_AddRefs(filteredIter));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Find the first text node in the range.
+  nsCOMPtr<nsIContent> content;
+  filteredIter->First();
+  if (!p1->IsText()) {
+    bool found = false;
+    for (; !filteredIter->IsDone(); filteredIter->Next()) {
+      nsINode* node = filteredIter->GetCurrentNode();
+      if (node->IsText()) {
+        p1 = node->AsText();
+        o1 = 0;
+        found = true;
+        break;
+      }
+    }
+    NS_ENSURE_TRUE(found, NS_ERROR_FAILURE);
+  }
+
+  // Find the last text node in the range.
+  filteredIter->Last();
+  if (!p2->IsText()) {
+    bool found = false;
+    for (; !filteredIter->IsDone(); filteredIter->Prev()) {
+      nsINode* node = filteredIter->GetCurrentNode();
+      if (node->IsText()) {
+        p2 = node->AsText();
+        o2 = p2->AsText()->Length();
+        found = true;
+
+        break;
+      }
+    }
+    NS_ENSURE_TRUE(found, NS_ERROR_FAILURE);
+  }
+
+  bool found = false;
+  *aSelLength = 0;
+
+  for (size_t i = 0; i < tableCount; i++) {
+    const UniquePtr<OffsetEntry>& entry = mOffsetTable[i];
+    LockOffsetEntryArrayLengthInDebugBuild(observer, mOffsetTable);
+    if (!found) {
+      if (entry->mTextNode == p1.get() &&
+          entry->OffsetInTextNodeIsInRangeOrEndOffset(o1)) {
+        *aSelOffset =
+            entry->mOffsetInTextInBlock + (o1 - entry->mOffsetInTextNode);
+        if (p1 == p2 && entry->OffsetInTextNodeIsInRangeOrEndOffset(o2)) {
+          // The start and end of the range are in the same offset
+          // entry. Calculate the length of the range then we're done.
+          *aSelLength = o2 - o1;
+          break;
+        }
+        // Add the length of the sub string in this offset entry
+        // that follows the start of the range.
+        *aSelLength = entry->EndOffsetInTextNode() - o1;
+        found = true;
+      }
+    } else {  // Found.
+      if (entry->mTextNode == p2.get() &&
+          entry->OffsetInTextNodeIsInRangeOrEndOffset(o2)) {
+        // We found the end of the range. Calculate the length of the
+        // sub string that is before the end of the range, then we're done.
+        *aSelLength += o2 - entry->mOffsetInTextNode;
+        break;
+      }
+      // The entire entry must be in the range.
+      *aSelLength += entry->mLength;
+    }
+  }
+
+  return NS_OK;
+}
+
+// static
+nsresult TextServicesDocument::GetRangeEndPoints(
+    const AbstractRange* aAbstractRange, nsINode** aStartContainer,
+    uint32_t* aStartOffset, nsINode** aEndContainer, uint32_t* aEndOffset) {
+  if (NS_WARN_IF(!aAbstractRange) || NS_WARN_IF(!aStartContainer) ||
+      NS_WARN_IF(!aEndContainer) || NS_WARN_IF(!aEndOffset)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsCOMPtr<nsINode> startContainer = aAbstractRange->GetStartContainer();
+  if (NS_WARN_IF(!startContainer)) {
+    return NS_ERROR_FAILURE;
+  }
+  nsCOMPtr<nsINode> endContainer = aAbstractRange->GetEndContainer();
+  if (NS_WARN_IF(!endContainer)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  startContainer.forget(aStartContainer);
+  endContainer.forget(aEndContainer);
+  *aStartOffset = aAbstractRange->StartOffset();
+  *aEndOffset = aAbstractRange->EndOffset();
+  return NS_OK;
+}
+
+// static
+nsresult TextServicesDocument::FirstTextNode(
+    FilteredContentIterator* aFilteredIter, IteratorStatus* aIteratorStatus) {
+  if (aIteratorStatus) {
+    *aIteratorStatus = IteratorStatus::eDone;
+  }
+
+  for (aFilteredIter->First(); !aFilteredIter->IsDone();
+       aFilteredIter->Next()) {
+    if (aFilteredIter->GetCurrentNode()->NodeType() == nsINode::TEXT_NODE) {
+      if (aIteratorStatus) {
+        *aIteratorStatus = IteratorStatus::eValid;
+      }
+      break;
+    }
+  }
+
+  return NS_OK;
+}
+
+// static
+nsresult TextServicesDocument::LastTextNode(
+    FilteredContentIterator* aFilteredIter, IteratorStatus* aIteratorStatus) {
+  if (aIteratorStatus) {
+    *aIteratorStatus = IteratorStatus::eDone;
+  }
+
+  for (aFilteredIter->Last(); !aFilteredIter->IsDone(); aFilteredIter->Prev()) {
+    if (aFilteredIter->GetCurrentNode()->NodeType() == nsINode::TEXT_NODE) {
+      if (aIteratorStatus) {
+        *aIteratorStatus = IteratorStatus::eValid;
+      }
+      break;
+    }
+  }
+
+  return NS_OK;
+}
+
+// static
+nsresult TextServicesDocument::FirstTextNodeInCurrentBlock(
+    FilteredContentIterator* aFilteredIter) {
+  NS_ENSURE_TRUE(aFilteredIter, NS_ERROR_NULL_POINTER);
+
+  ClearDidSkip(aFilteredIter);
+
+  // Walk backwards over adjacent text nodes until
+  // we hit a block boundary:
+  RefPtr<Text> lastTextNode;
+  while (!aFilteredIter->IsDone()) {
+    nsCOMPtr<nsIContent> content =
+        aFilteredIter->GetCurrentNode()->IsContent()
+            ? aFilteredIter->GetCurrentNode()->AsContent()
+            : nullptr;
+    // We don't observe layout updates, therefore, we should consider whether
+    // block or inline only with the default definition of the element.
+    if (lastTextNode && content &&
+        (HTMLEditUtils::IsBlockElement(*content,
+                                       BlockInlineCheck::UseHTMLDefaultStyle) ||
+         content->IsHTMLElement(nsGkAtoms::br))) {
+      break;
+    }
+    if (content && content->IsText()) {
+      if (lastTextNode && !TextServicesDocument::HasSameBlockNodeParent(
+                              *content->AsText(), *lastTextNode)) {
+        // We're done, the current text node is in a
+        // different block.
+        break;
+      }
+      lastTextNode = content->AsText();
+    }
+
+    aFilteredIter->Prev();
+
+    if (DidSkip(aFilteredIter)) {
+      break;
+    }
+  }
+
+  if (lastTextNode) {
+    aFilteredIter->PositionAt(lastTextNode);
+  }
+
+  // XXX: What should we return if last is null?
+
+  return NS_OK;
+}
+
+// static
+nsresult TextServicesDocument::FirstTextNodeInPrevBlock(
+    FilteredContentIterator* aFilteredIter) {
+  NS_ENSURE_TRUE(aFilteredIter, NS_ERROR_NULL_POINTER);
+
+  // XXX: What if mFilteredIter is not currently on a text node?
+
+  // Make sure mFilteredIter is pointing to the first text node in the
+  // current block:
+
+  nsresult rv = FirstTextNodeInCurrentBlock(aFilteredIter);
+
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  // Point mFilteredIter to the first node before the first text node:
+
+  aFilteredIter->Prev();
+
+  if (aFilteredIter->IsDone()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Now find the first text node of the next block:
+
+  return FirstTextNodeInCurrentBlock(aFilteredIter);
+}
+
+// static
+nsresult TextServicesDocument::FirstTextNodeInNextBlock(
+    FilteredContentIterator* aFilteredIter) {
+  bool crossedBlockBoundary = false;
+
+  NS_ENSURE_TRUE(aFilteredIter, NS_ERROR_NULL_POINTER);
+
+  ClearDidSkip(aFilteredIter);
+
+  RefPtr<Text> previousTextNode;
+  while (!aFilteredIter->IsDone()) {
+    if (nsCOMPtr<nsIContent> content =
+            aFilteredIter->GetCurrentNode()->IsContent()
+                ? aFilteredIter->GetCurrentNode()->AsContent()
+                : nullptr) {
+      if (content->IsText()) {
+        if (crossedBlockBoundary ||
+            (previousTextNode && !TextServicesDocument::HasSameBlockNodeParent(
+                                     *previousTextNode, *content->AsText()))) {
+          break;
+        }
+        previousTextNode = content->AsText();
+      }
+      // We don't observe layout updates, therefore, we should consider whether
+      // block or inline only with the default definition of the element.
+      else if (!crossedBlockBoundary &&
+               (HTMLEditUtils::IsBlockElement(
+                    *content, BlockInlineCheck::UseHTMLDefaultStyle) ||
+                content->IsHTMLElement(nsGkAtoms::br))) {
+        crossedBlockBoundary = true;
+      }
+    }
+
+    aFilteredIter->Next();
+
+    if (!crossedBlockBoundary && DidSkip(aFilteredIter)) {
+      crossedBlockBoundary = true;
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult TextServicesDocument::GetFirstTextNodeInPrevBlock(
+    nsIContent** aContent) {
+  NS_ENSURE_TRUE(aContent, NS_ERROR_NULL_POINTER);
+
+  *aContent = 0;
+
+  // Save the iterator's current content node so we can restore
+  // it when we are done:
+
+  nsINode* node = mFilteredIter->GetCurrentNode();
+
+  nsresult rv = FirstTextNodeInPrevBlock(mFilteredIter);
+
+  if (NS_FAILED(rv)) {
+    // Try to restore the iterator before returning.
+    mFilteredIter->PositionAt(node);
+    return rv;
+  }
+
+  if (!mFilteredIter->IsDone()) {
+    nsCOMPtr<nsIContent> current =
+        mFilteredIter->GetCurrentNode()->IsContent()
+            ? mFilteredIter->GetCurrentNode()->AsContent()
+            : nullptr;
+    current.forget(aContent);
+  }
+
+  // Restore the iterator:
+
+  return mFilteredIter->PositionAt(node);
+}
+
+nsresult TextServicesDocument::GetFirstTextNodeInNextBlock(
+    nsIContent** aContent) {
+  NS_ENSURE_TRUE(aContent, NS_ERROR_NULL_POINTER);
+
+  *aContent = 0;
+
+  // Save the iterator's current content node so we can restore
+  // it when we are done:
+
+  nsINode* node = mFilteredIter->GetCurrentNode();
+
+  nsresult rv = FirstTextNodeInNextBlock(mFilteredIter);
+
+  if (NS_FAILED(rv)) {
+    // Try to restore the iterator before returning.
+    mFilteredIter->PositionAt(node);
+    return rv;
+  }
+
+  if (!mFilteredIter->IsDone()) {
+    nsCOMPtr<nsIContent> current =
+        mFilteredIter->GetCurrentNode()->IsContent()
+            ? mFilteredIter->GetCurrentNode()->AsContent()
+            : nullptr;
+    current.forget(aContent);
+  }
+
+  // Restore the iterator:
+  return mFilteredIter->PositionAt(node);
+}
+
+Result<TextServicesDocument::IteratorStatus, nsresult>
+TextServicesDocument::OffsetEntryArray::Init(
+    FilteredContentIterator& aFilteredIter, IteratorStatus aIteratorStatus,
+    nsRange* aIterRange, nsAString* aAllTextInBlock /* = nullptr */) {
+  Clear();
+
+  if (aAllTextInBlock) {
+    aAllTextInBlock->Truncate();
+  }
+
+  if (aIteratorStatus == IteratorStatus::eDone) {
+    return IteratorStatus::eDone;
+  }
+
+  // If we have an aIterRange, retrieve the endpoints so
+  // they can be used in the while loop below to trim entries
+  // for text nodes that are partially selected by aIterRange.
+
+  nsCOMPtr<nsINode> rngStartNode, rngEndNode;
+  uint32_t rngStartOffset = 0, rngEndOffset = 0;
+  if (aIterRange) {
+    nsresult rv = TextServicesDocument::GetRangeEndPoints(
+        aIterRange, getter_AddRefs(rngStartNode), &rngStartOffset,
+        getter_AddRefs(rngEndNode), &rngEndOffset);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("TextServicesDocument::GetRangeEndPoints() failed");
+      return Err(rv);
+    }
+  }
+
+  // The text service could have added text nodes to the beginning
+  // of the current block and called this method again. Make sure
+  // we really are at the beginning of the current block:
+
+  nsresult rv =
+      TextServicesDocument::FirstTextNodeInCurrentBlock(&aFilteredIter);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("TextServicesDocument::FirstTextNodeInCurrentBlock() failed");
+    return Err(rv);
+  }
+
+  TextServicesDocument::ClearDidSkip(&aFilteredIter);
+
+  uint32_t offset = 0;
+  RefPtr<Text> firstTextNode, previousTextNode;
+  while (!aFilteredIter.IsDone()) {
+    if (nsCOMPtr<nsIContent> content =
+            aFilteredIter.GetCurrentNode()->IsContent()
+                ? aFilteredIter.GetCurrentNode()->AsContent()
+                : nullptr) {
+      // We don't observe layout updates, therefore, we should consider whether
+      // block or inline only with the default definition of the element.
+      if (HTMLEditUtils::IsBlockElement(
+              *content, BlockInlineCheck::UseHTMLDefaultStyle) ||
+          content->IsHTMLElement(nsGkAtoms::br)) {
+        break;
+      }
+      if (content->IsText()) {
+        if (previousTextNode && !TextServicesDocument::HasSameBlockNodeParent(
+                                    *previousTextNode, *content->AsText())) {
+          break;
+        }
+
+        nsString str;
+        content->AsText()->GetNodeValue(str);
+
+        // Add an entry for this text node into the offset table:
+
+        UniquePtr<OffsetEntry>& entry = *AppendElement(
+            MakeUnique<OffsetEntry>(*content->AsText(), offset, str.Length()));
+        LockOffsetEntryArrayLengthInDebugBuild(observer, *this);
+
+        // If one or both of the endpoints of the iteration range
+        // are in the text node for this entry, make sure the entry
+        // only accounts for the portion of the text node that is
+        // in the range.
+
+        uint32_t startOffset = 0;
+        uint32_t endOffset = str.Length();
+        bool adjustStr = false;
+
+        if (entry->mTextNode == rngStartNode) {
+          entry->mOffsetInTextNode = startOffset = rngStartOffset;
+          adjustStr = true;
+        }
+
+        if (entry->mTextNode == rngEndNode) {
+          endOffset = rngEndOffset;
+          adjustStr = true;
+        }
+
+        if (adjustStr) {
+          entry->mLength = endOffset - startOffset;
+          str = Substring(str, startOffset, entry->mLength);
+        }
+
+        offset += str.Length();
+
+        if (aAllTextInBlock) {
+          // Append the text node's string to the output string:
+          if (!firstTextNode) {
+            *aAllTextInBlock = str;
+          } else {
+            *aAllTextInBlock += str;
+          }
+        }
+
+        previousTextNode = content->AsText();
+
+        if (!firstTextNode) {
+          firstTextNode = content->AsText();
+        }
+      }
+    }
+
+    aFilteredIter.Next();
+
+    if (TextServicesDocument::DidSkip(&aFilteredIter)) {
+      break;
+    }
+  }
+
+  if (firstTextNode) {
+    // Always leave the iterator pointing at the first
+    // text node of the current block!
+    aFilteredIter.PositionAt(firstTextNode);
+    return aIteratorStatus;
+  }
+
+  // If we never ran across a text node, the iterator
+  // might have been pointing to something invalid to
+  // begin with.
+  return IteratorStatus::eDone;
+}
+
+void TextServicesDocument::OffsetEntryArray::RemoveInvalidElements() {
+  for (size_t i = 0; i < Length();) {
+    if (ElementAt(i)->mIsValid) {
+      i++;
+      continue;
+    }
+
+    RemoveElementAt(i);
+    if (!mSelection.IsSet()) {
+      continue;
+    }
+    if (mSelection.StartIndex() == i) {
+      NS_ASSERTION(false, "What should we do in this case?");
+      mSelection.Reset();
+    } else if (mSelection.StartIndex() > i) {
+      MOZ_DIAGNOSTIC_ASSERT(mSelection.StartIndex() - 1 < Length());
+      MOZ_DIAGNOSTIC_ASSERT(mSelection.EndIndex() - 1 < Length());
+      mSelection.SetIndexes(mSelection.StartIndex() - 1,
+                            mSelection.EndIndex() - 1);
+    } else if (mSelection.EndIndex() >= i) {
+      MOZ_DIAGNOSTIC_ASSERT(mSelection.EndIndex() - 1 < Length());
+      mSelection.SetIndexes(mSelection.StartIndex(), mSelection.EndIndex() - 1);
+    }
+  }
+}
+
+nsresult TextServicesDocument::OffsetEntryArray::SplitElementAt(
+    size_t aIndex, uint32_t aOffsetInTextNode) {
+  OffsetEntry* leftEntry = ElementAt(aIndex).get();
+  MOZ_ASSERT(leftEntry);
+  NS_ASSERTION((aOffsetInTextNode > 0), "aOffsetInTextNode == 0");
+  NS_ASSERTION((aOffsetInTextNode < leftEntry->mLength),
+               "aOffsetInTextNode >= mLength");
+
+  if (aOffsetInTextNode < 1 || aOffsetInTextNode >= leftEntry->mLength) {
+    return NS_ERROR_FAILURE;
+  }
+
+  const uint32_t oldLength = leftEntry->mLength - aOffsetInTextNode;
+
+  // XXX(Bug 1631371) Check if this should use a fallible operation as it
+  // pretended earlier.
+  UniquePtr<OffsetEntry>& rightEntry = *InsertElementAt(
+      aIndex + 1,
+      MakeUnique<OffsetEntry>(leftEntry->mTextNode,
+                              leftEntry->mOffsetInTextInBlock + oldLength,
+                              aOffsetInTextNode));
+  LockOffsetEntryArrayLengthInDebugBuild(observer, *this);
+  leftEntry->mLength = oldLength;
+  rightEntry->mOffsetInTextNode = leftEntry->mOffsetInTextNode + oldLength;
+
+  return NS_OK;
+}
+
+Maybe<size_t> TextServicesDocument::OffsetEntryArray::FirstIndexOf(
+    const Text& aTextNode) const {
+  for (size_t i = 0; i < Length(); i++) {
+    if (ElementAt(i)->mTextNode == &aTextNode) {
+      return Some(i);
+    }
+  }
+  return Nothing();
+}
+
+// Spellchecker code has this. See bug 211343
+#define IS_NBSP_CHAR(c) (((unsigned char)0xa0) == (c))
+
+Result<EditorDOMRangeInTexts, nsresult>
+TextServicesDocument::OffsetEntryArray::FindWordRange(
+    nsAString& aAllTextInBlock, const EditorRawDOMPoint& aStartPointToScan) {
+  MOZ_ASSERT(aStartPointToScan.IsInTextNode());
+  // It's assumed that aNode is a text node. The first thing
+  // we do is get its index in the offset table so we can
+  // calculate the dom point's string offset.
+  Maybe<size_t> maybeEntryIndex =
+      FirstIndexOf(*aStartPointToScan.ContainerAs<Text>());
+  if (NS_WARN_IF(maybeEntryIndex.isNothing())) {
+    NS_WARNING(
+        "TextServicesDocument::OffsetEntryArray::FirstIndexOf() didn't find "
+        "entries");
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  // Next we map offset into a string offset.
+
+  const UniquePtr<OffsetEntry>& entry = ElementAt(*maybeEntryIndex);
+  LockOffsetEntryArrayLengthInDebugBuild(observer, *this);
+  uint32_t strOffset = entry->mOffsetInTextInBlock +
+                       aStartPointToScan.Offset() - entry->mOffsetInTextNode;
+
+  // Now we use the word breaker to find the beginning and end
+  // of the word from our calculated string offset.
+
+  const char16_t* str = aAllTextInBlock.BeginReading();
+  MOZ_ASSERT(strOffset <= aAllTextInBlock.Length(),
+             "The string offset shouldn't be greater than the string length!");
+
+  intl::WordRange res = intl::WordBreaker::FindWord(aAllTextInBlock, strOffset);
+
+  // Strip out the NBSPs at the ends
+  while (res.mBegin <= res.mEnd && IS_NBSP_CHAR(str[res.mBegin])) {
+    res.mBegin++;
+  }
+  if (str[res.mEnd] == static_cast<char16_t>(0x20)) {
+    uint32_t realEndWord = res.mEnd - 1;
+    while (realEndWord > res.mBegin && IS_NBSP_CHAR(str[realEndWord])) {
+      realEndWord--;
+    }
+    if (realEndWord < res.mEnd - 1) {
+      res.mEnd = realEndWord + 1;
+    }
+  }
+
+  // Now that we have the string offsets for the beginning
+  // and end of the word, run through the offset table and
+  // convert them back into dom points.
+
+  EditorDOMPointInText wordStart, wordEnd;
+  size_t lastIndex = Length() - 1;
+  for (size_t i = 0; i <= lastIndex; i++) {
+    // Check to see if res.mBegin is within the range covered
+    // by this entry. Note that if res.mBegin is after the last
+    // character covered by this entry, we will use the next
+    // entry if there is one.
+    const UniquePtr<OffsetEntry>& entry = ElementAt(i);
+    LockOffsetEntryArrayLengthInDebugBuild(observer, *this);
+    if (entry->mOffsetInTextInBlock <= res.mBegin &&
+        (res.mBegin < entry->EndOffsetInTextInBlock() ||
+         (res.mBegin == entry->EndOffsetInTextInBlock() && i == lastIndex))) {
+      wordStart.Set(entry->mTextNode, entry->mOffsetInTextNode + res.mBegin -
+                                          entry->mOffsetInTextInBlock);
+    }
+
+    // Check to see if res.mEnd is within the range covered
+    // by this entry.
+    if (entry->mOffsetInTextInBlock <= res.mEnd &&
+        res.mEnd <= entry->EndOffsetInTextInBlock()) {
+      if (res.mBegin == res.mEnd &&
+          res.mEnd == entry->EndOffsetInTextInBlock() && i != lastIndex) {
+        // Wait for the next round so that we use the same entry
+        // we did for aWordStartNode.
+        continue;
+      }
+
+      wordEnd.Set(entry->mTextNode, entry->mOffsetInTextNode + res.mEnd -
+                                        entry->mOffsetInTextInBlock);
+      break;
+    }
+  }
+
+  return EditorDOMRangeInTexts(wordStart, wordEnd);
+}
+
+/**
+ * nsIEditActionListener implementation:
+ *   Don't implement the behavior directly here.  The methods won't be called
+ *   if the instance is created for inline spell checker created for editor.
+ *   If you need to listen a new edit action, you need to add similar
+ *   non-virtual method and you need to call it from EditorBase directly.
+ */
+
+NS_IMETHODIMP
+TextServicesDocument::DidDeleteNode(nsINode* aChild, nsresult aResult) {
+  if (NS_WARN_IF(NS_FAILED(aResult)) || NS_WARN_IF(!aChild) ||
+      !aChild->IsContent()) {
+    return NS_OK;
+  }
+  DidDeleteContent(*aChild->AsContent());
+  return NS_OK;
+}
+
+NS_IMETHODIMP TextServicesDocument::DidJoinContents(
+    const EditorRawDOMPoint& aJoinedPoint, const nsINode* aRemovedNode) {
+  if (MOZ_UNLIKELY(NS_WARN_IF(!aJoinedPoint.IsSetAndValid()) ||
+                   NS_WARN_IF(!aRemovedNode->IsContent()))) {
+    return NS_OK;
+  }
+  DidJoinContents(aJoinedPoint, *aRemovedNode->AsContent());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+TextServicesDocument::DidInsertText(CharacterData* aTextNode, int32_t aOffset,
+                                    const nsAString& aString,
+                                    nsresult aResult) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+TextServicesDocument::WillDeleteText(CharacterData* aTextNode, int32_t aOffset,
+                                     int32_t aLength) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+TextServicesDocument::WillDeleteRanges(
+    const nsTArray<RefPtr<nsRange>>& aRangesToDelete) {
+  return NS_OK;
+}
+
+#undef LockOffsetEntryArrayLengthInDebugBuild
+
+}  // namespace mozilla
diff --git a/editor/spellchecker/TextServicesDocument.h b/editor/spellchecker/TextServicesDocument.h
new file mode 100644
index 0000000000..0b72bda977
--- /dev/null
+++ b/editor/spellchecker/TextServicesDocument.h
@@ -0,0 +1,436 @@
+/* -*- Mode: C++; tab-width: 2; 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 mozilla_TextServicesDocument_h
+#define mozilla_TextServicesDocument_h
+
+#include "mozilla/Maybe.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCOMPtr.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsIEditActionListener.h"
+#include "nsISupportsImpl.h"
+#include "nsStringFwd.h"
+#include "nsTArray.h"
+#include "nscore.h"
+
+class nsIContent;
+class nsIEditor;
+class nsINode;
+class nsISelectionController;
+class nsRange;
+
+namespace mozilla {
+
+class EditorBase;
+class FilteredContentIterator;
+class OffsetEntry;
+
+namespace dom {
+class AbstractRange;
+class Document;
+class Element;
+class StaticRange;
+};  // namespace dom
+
+/**
+ * The TextServicesDocument presents the document in as a bunch of flattened
+ * text blocks. Each text block can be retrieved as an nsString.
+ */
+class TextServicesDocument final : public nsIEditActionListener {
+ private:
+  enum class IteratorStatus : uint8_t {
+    // No iterator (I), or iterator doesn't point to anything valid.
+    eDone = 0,
+    // I points to first text node (TN) in current block (CB).
+    eValid,
+    // No TN in CB, I points to first TN in prev block.
+    ePrev,
+    // No TN in CB, I points to first TN in next block.
+    eNext,
+  };
+
+  class OffsetEntryArray final : public nsTArray<UniquePtr<OffsetEntry>> {
+   public:
+    /**
+     * Init() initializes this array with aFilteredIter.
+     *
+     * @param[in]  aIterRange   Can be nullptr.
+     * @param[out] aAllTextInBlock
+     *                          Returns all text in the block.
+     */
+    Result<IteratorStatus, nsresult> Init(
+        FilteredContentIterator& aFilteredIter, IteratorStatus aIteratorStatus,
+        nsRange* aIterRange, nsAString* aAllTextInBlock = nullptr);
+
+    /**
+     * Returns index of first `OffsetEntry` which manages aTextNode.
+     */
+    Maybe<size_t> FirstIndexOf(const dom::Text& aTextNode) const;
+
+    /**
+     * FindWordRange() returns a word range starting from aStartPointToScan
+     * in aAllTextInBlock.
+     */
+    Result<EditorDOMRangeInTexts, nsresult> FindWordRange(
+        nsAString& aAllTextInBlock, const EditorRawDOMPoint& aStartPointToScan);
+
+    /**
+     * SplitElementAt() splits an `OffsetEntry` at aIndex if aOffsetInTextNode
+     * is middle of the range in the text node.
+     *
+     * @param aIndex    Index of the entry which you want to split.
+     * @param aOffsetInTextNode
+     *                  Offset in the text node.  I.e., the offset should be
+     *                  greater than 0 and less than `mLength`.
+     */
+    nsresult SplitElementAt(size_t aIndex, uint32_t aOffsetInTextNode);
+
+    /**
+     * Remove all `OffsetEntry` elements whose `mIsValid` is set to false.
+     */
+    void RemoveInvalidElements();
+
+    /**
+     * Called when non-collapsed selection will be deleted.
+     */
+    nsresult WillDeleteSelection();
+
+    /**
+     * Called when non-collapsed selection is deleteded.
+     */
+    OffsetEntry* DidDeleteSelection();
+
+    /**
+     * Called when aInsertedText is inserted.
+     */
+    MOZ_CAN_RUN_SCRIPT nsresult DidInsertText(dom::Selection* aSelection,
+                                              const nsAString& aInsertedString);
+
+    /**
+     * Called when selection range will be applied to the DOM Selection.
+     */
+    Result<EditorRawDOMRangeInTexts, nsresult> WillSetSelection(
+        uint32_t aOffsetInTextInBlock, uint32_t aLength);
+
+    class Selection final {
+     public:
+      size_t StartIndex() const {
+        MOZ_ASSERT(IsIndexesSet());
+        return *mStartIndex;
+      }
+      size_t EndIndex() const {
+        MOZ_ASSERT(IsIndexesSet());
+        return *mEndIndex;
+      }
+
+      uint32_t StartOffsetInTextInBlock() const {
+        MOZ_ASSERT(IsSet());
+        return *mStartOffsetInTextInBlock;
+      }
+      uint32_t EndOffsetInTextInBlock() const {
+        MOZ_ASSERT(IsSet());
+        return *mEndOffsetInTextInBlock;
+      }
+      uint32_t LengthInTextInBlock() const {
+        MOZ_ASSERT(IsSet());
+        return *mEndOffsetInTextInBlock - *mStartOffsetInTextInBlock;
+      }
+
+      bool IsCollapsed() {
+        return !IsSet() || (IsInSameElement() && StartOffsetInTextInBlock() ==
+                                                     EndOffsetInTextInBlock());
+      }
+
+      bool IsIndexesSet() const {
+        return mStartIndex.isSome() && mEndIndex.isSome();
+      }
+      bool IsSet() const {
+        return IsIndexesSet() && mStartOffsetInTextInBlock.isSome() &&
+               mEndOffsetInTextInBlock.isSome();
+      }
+      bool IsInSameElement() const {
+        return IsIndexesSet() && StartIndex() == EndIndex();
+      }
+
+      void Reset() {
+        mStartIndex.reset();
+        mEndIndex.reset();
+        mStartOffsetInTextInBlock.reset();
+        mEndOffsetInTextInBlock.reset();
+      }
+      void SetIndex(size_t aIndex) { mEndIndex = mStartIndex = Some(aIndex); }
+      void Set(size_t aIndex, uint32_t aOffsetInTextInBlock) {
+        mEndIndex = mStartIndex = Some(aIndex);
+        mStartOffsetInTextInBlock = mEndOffsetInTextInBlock =
+            Some(aOffsetInTextInBlock);
+      }
+      void SetIndexes(size_t aStartIndex, size_t aEndIndex) {
+        MOZ_DIAGNOSTIC_ASSERT(aStartIndex <= aEndIndex);
+        mStartIndex = Some(aStartIndex);
+        mEndIndex = Some(aEndIndex);
+      }
+      void Set(size_t aStartIndex, size_t aEndIndex,
+               uint32_t aStartOffsetInTextInBlock,
+               uint32_t aEndOffsetInTextInBlock) {
+        MOZ_DIAGNOSTIC_ASSERT(aStartIndex <= aEndIndex);
+        mStartIndex = Some(aStartIndex);
+        mEndIndex = Some(aEndIndex);
+        mStartOffsetInTextInBlock = Some(aStartOffsetInTextInBlock);
+        mEndOffsetInTextInBlock = Some(aEndOffsetInTextInBlock);
+      }
+
+      void CollapseToStart() {
+        MOZ_ASSERT(mStartIndex.isSome());
+        MOZ_ASSERT(mStartOffsetInTextInBlock.isSome());
+        mEndIndex = mStartIndex;
+        mEndOffsetInTextInBlock = mStartOffsetInTextInBlock;
+      }
+
+     private:
+      Maybe<size_t> mStartIndex;
+      Maybe<size_t> mEndIndex;
+      // Selected start and end offset in all text in a block element.
+      Maybe<uint32_t> mStartOffsetInTextInBlock;
+      Maybe<uint32_t> mEndOffsetInTextInBlock;
+    };
+    Selection mSelection;
+  };
+
+  RefPtr<dom::Document> mDocument;
+  nsCOMPtr<nsISelectionController> mSelCon;
+  RefPtr<EditorBase> mEditorBase;
+  RefPtr<FilteredContentIterator> mFilteredIter;
+  nsCOMPtr<nsIContent> mPrevTextBlock;
+  nsCOMPtr<nsIContent> mNextTextBlock;
+  OffsetEntryArray mOffsetTable;
+  RefPtr<nsRange> mExtent;
+
+  uint32_t mTxtSvcFilterType;
+  IteratorStatus mIteratorStatus;
+
+ protected:
+  virtual ~TextServicesDocument() = default;
+
+ public:
+  TextServicesDocument();
+
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_CLASS(TextServicesDocument)
+
+  /**
+   * Initializes the text services document to use a particular editor. The
+   * text services document will use the DOM document and presentation shell
+   * used by the editor.
+   *
+   * @param aEditor             The editor to use.
+   */
+  nsresult InitWithEditor(nsIEditor* aEditor);
+
+  /**
+   * Sets the range/extent over which the text services document will iterate.
+   * Note that InitWithEditor() should have been called prior to calling this
+   * method.  If this method is never called, the text services defaults to
+   * iterating over the entire document.
+   *
+   * @param aAbstractRange      The range to use. aAbstractRange must point to a
+   *                            valid range object.
+   */
+  nsresult SetExtent(const dom::AbstractRange* aAbstractRange);
+
+  /**
+   * Expands the end points of the range so that it spans complete words.  This
+   * call does not change any internal state of the text services document.
+   *
+   * @param aStaticRange        [in/out] The range to be expanded/adjusted.
+   */
+  nsresult ExpandRangeToWordBoundaries(dom::StaticRange* aStaticRange);
+
+  /**
+   * Sets the filter type to be used while iterating over content.
+   * This will clear the current filter type if it's not either
+   * FILTERTYPE_NORMAL or FILTERTYPE_MAIL.
+   *
+   * @param aFilterType         The filter type to be used while iterating over
+   *                            content.
+   */
+  nsresult SetFilterType(uint32_t aFilterType);
+
+  /**
+   * Returns the text in the current text block.
+   *
+   * @param aStr                [OUT] This will contain the text.
+   */
+  nsresult GetCurrentTextBlock(nsAString& aStr);
+
+  /**
+   * Tells the document to point to the first text block in the document.  This
+   * method does not adjust the current cursor position or selection.
+   */
+  nsresult FirstBlock();
+
+  enum class BlockSelectionStatus {
+    // There is no text block (TB) in or before the selection (S).
+    eBlockNotFound = 0,
+    // No TB in S, but found one before/after S.
+    eBlockOutside,
+    // S extends beyond the start and end of TB.
+    eBlockInside,
+    // TB contains entire S.
+    eBlockContains,
+    // S begins or ends in TB but extends outside of TB.
+    eBlockPartial,
+  };
+
+  /**
+   * Tells the document to point to the last text block that contains the
+   * current selection or caret.
+   *
+   * @param aSelectionStatus    [OUT] This will contain the text block
+   *                            selection status.
+   * @param aSelectionOffset    [OUT] This will contain the offset into the
+   *                            string returned by GetCurrentTextBlock() where
+   *                            the selection begins.
+   * @param aLength             [OUT] This will contain the number of
+   *                            characters that are selected in the string.
+   */
+  MOZ_CAN_RUN_SCRIPT
+  nsresult LastSelectedBlock(BlockSelectionStatus* aSelStatus,
+                             uint32_t* aSelOffset, uint32_t* aSelLength);
+
+  /**
+   * Tells the document to point to the text block before the current one.
+   * This method will return NS_OK, even if there is no previous block.
+   * Callers should call IsDone() to check if we have gone beyond the first
+   * text block in the document.
+   */
+  nsresult PrevBlock();
+
+  /**
+   * Tells the document to point to the text block after the current one.
+   * This method will return NS_OK, even if there is no next block. Callers
+   * should call IsDone() to check if we have gone beyond the last text block
+   * in the document.
+   */
+  nsresult NextBlock();
+
+  /**
+   * IsDone() will always set aIsDone == false unless the document contains
+   * no text, PrevBlock() was called while the document was already pointing
+   * to the first text block in the document, or NextBlock() was called while
+   * the document was already pointing to the last text block in the document.
+   *
+   * @param aIsDone             [OUT] This will contain the result.
+   */
+  nsresult IsDone(bool* aIsDone);
+
+  /**
+   * SetSelection() allows the caller to set the selection based on an offset
+   * into the string returned by GetCurrentTextBlock().  A length of zero
+   * places the cursor at that offset. A positive non-zero length "n" selects
+   * n characters in the string.
+   *
+   * @param aOffset             Offset into string returned by
+   *                            GetCurrentTextBlock().
+   * @param aLength             Number of characters selected.
+   */
+  MOZ_CAN_RUN_SCRIPT nsresult SetSelection(uint32_t aOffset, uint32_t aLength);
+
+  /**
+   * Scrolls the document so that the current selection is visible.
+   */
+  nsresult ScrollSelectionIntoView();
+
+  /**
+   * Deletes the text selected by SetSelection(). Calling DeleteSelection()
+   * with nothing selected, or with a collapsed selection (cursor) does
+   * nothing and returns NS_OK.
+   */
+  MOZ_CAN_RUN_SCRIPT
+  nsresult DeleteSelection();
+
+  /**
+   * Inserts the given text at the current cursor position.  If there is a
+   * selection, it will be deleted before the text is inserted.
+   */
+  MOZ_CAN_RUN_SCRIPT
+  nsresult InsertText(const nsAString& aText);
+
+  /**
+   * nsIEditActionListener method implementations.
+   */
+  NS_DECL_NSIEDITACTIONLISTENER
+
+  /**
+   * Actual edit action listeners.  When you add new method here for listening
+   * to new edit action, you need to make it called by EditorBase.
+   * Additionally, you need to call it from proper method of
+   * nsIEditActionListener too because if this is created not for inline
+   * spell checker of the editor, edit actions will be notified via
+   * nsIEditActionListener (slow path, though).
+   */
+  void DidDeleteContent(const nsIContent& aChildContent);
+  void DidJoinContents(const EditorRawDOMPoint& aJoinedPoint,
+                       const nsIContent& aRemovedContent);
+
+ private:
+  // TODO: We should get rid of this method since `aAbstractRange` has
+  //       enough simple API to get them.
+  static nsresult GetRangeEndPoints(const dom::AbstractRange* aAbstractRange,
+                                    nsINode** aStartContainer,
+                                    uint32_t* aStartOffset,
+                                    nsINode** aEndContainer,
+                                    uint32_t* aEndOffset);
+
+  nsresult CreateFilteredContentIterator(
+      const dom::AbstractRange* aAbstractRange,
+      FilteredContentIterator** aFilteredIter);
+
+  dom::Element* GetDocumentContentRootNode() const;
+  already_AddRefed<nsRange> CreateDocumentContentRange();
+  already_AddRefed<nsRange> CreateDocumentContentRootToNodeOffsetRange(
+      nsINode* aParent, uint32_t aOffset, bool aToStart);
+  nsresult CreateDocumentContentIterator(
+      FilteredContentIterator** aFilteredIter);
+
+  nsresult AdjustContentIterator();
+
+  static nsresult FirstTextNode(FilteredContentIterator* aFilteredIter,
+                                IteratorStatus* aIteratorStatus);
+  static nsresult LastTextNode(FilteredContentIterator* aFilteredIter,
+                               IteratorStatus* aIteratorStatus);
+
+  static nsresult FirstTextNodeInCurrentBlock(
+      FilteredContentIterator* aFilteredIter);
+  static nsresult FirstTextNodeInPrevBlock(
+      FilteredContentIterator* aFilteredIter);
+  static nsresult FirstTextNodeInNextBlock(
+      FilteredContentIterator* aFilteredIter);
+
+  nsresult GetFirstTextNodeInPrevBlock(nsIContent** aContent);
+  nsresult GetFirstTextNodeInNextBlock(nsIContent** aContent);
+
+  static bool DidSkip(FilteredContentIterator* aFilteredIter);
+  static void ClearDidSkip(FilteredContentIterator* aFilteredIter);
+
+  static bool HasSameBlockNodeParent(dom::Text& aTextNode1,
+                                     dom::Text& aTextNode2);
+
+  MOZ_CAN_RUN_SCRIPT nsresult SetSelectionInternal(uint32_t aOffset,
+                                                   uint32_t aLength,
+                                                   bool aDoUpdate);
+  MOZ_CAN_RUN_SCRIPT nsresult GetSelection(BlockSelectionStatus* aSelStatus,
+                                           uint32_t* aSelOffset,
+                                           uint32_t* aSelLength);
+  MOZ_CAN_RUN_SCRIPT nsresult
+  GetCollapsedSelection(BlockSelectionStatus* aSelStatus, uint32_t* aSelOffset,
+                        uint32_t* aSelLength);
+  nsresult GetUncollapsedSelection(BlockSelectionStatus* aSelStatus,
+                                   uint32_t* aSelOffset, uint32_t* aSelLength);
+};
+
+}  // namespace mozilla
+
+#endif  // #ifndef mozilla_TextServicesDocument_h
diff --git a/editor/spellchecker/moz.build b/editor/spellchecker/moz.build
new file mode 100644
index 0000000000..cd3d58df7e
--- /dev/null
+++ b/editor/spellchecker/moz.build
@@ -0,0 +1,34 @@
+# -*- 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/.
+
+MOCHITEST_MANIFESTS += ["tests/mochitest.toml"]
+
+MOCHITEST_CHROME_MANIFESTS += ["tests/chrome.toml"]
+
+XPIDL_SOURCES += [
+    "nsIInlineSpellChecker.idl",
+]
+
+XPIDL_MODULE = "txtsvc"
+
+EXPORTS.mozilla += [
+    "EditorSpellCheck.h",
+    "TextServicesDocument.h",
+]
+
+UNIFIED_SOURCES += [
+    "EditorSpellCheck.cpp",
+    "FilteredContentIterator.cpp",
+    "nsComposeTxtSrvFilter.cpp",
+    "TextServicesDocument.cpp",
+]
+
+LOCAL_INCLUDES += [
+    # For stop exposing libeditor's headers, allow to refer them directly
+    "/editor/libeditor",
+]
+
+FINAL_LIBRARY = "xul"
diff --git a/editor/spellchecker/nsComposeTxtSrvFilter.cpp b/editor/spellchecker/nsComposeTxtSrvFilter.cpp
new file mode 100644
index 0000000000..7ab6eae8cb
--- /dev/null
+++ b/editor/spellchecker/nsComposeTxtSrvFilter.cpp
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 2; 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 "nsComposeTxtSrvFilter.h"
+#include "nsError.h"              // for NS_OK
+#include "nsIContent.h"           // for nsIContent
+#include "nsLiteralString.h"      // for NS_LITERAL_STRING
+#include "mozilla/dom/Element.h"  // for nsIContent
+
+using namespace mozilla;
+
+bool nsComposeTxtSrvFilter::Skip(nsINode* aNode) const {
+  if (NS_WARN_IF(!aNode)) {
+    return false;
+  }
+
+  // Check to see if we can skip this node
+
+  if (aNode->IsAnyOfHTMLElements(nsGkAtoms::script, nsGkAtoms::textarea,
+                                 nsGkAtoms::select, nsGkAtoms::style,
+                                 nsGkAtoms::map)) {
+    return true;
+  }
+
+  if (!mIsForMail) {
+    return false;
+  }
+
+  // For nodes that are blockquotes, we must make sure
+  // their type is "cite"
+  if (aNode->IsHTMLElement(nsGkAtoms::blockquote)) {
+    return aNode->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::type,
+                                           nsGkAtoms::cite, eIgnoreCase);
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::span)) {
+    if (aNode->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::mozquote,
+                                        nsGkAtoms::_true, eIgnoreCase)) {
+      return true;
+    }
+
+    return aNode->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::_class,
+                                           nsGkAtoms::mozsignature,
+                                           eCaseMatters);
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::table)) {
+    return aNode->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::_class,
+                                           u"moz-email-headers-table"_ns,
+                                           eCaseMatters);
+  }
+
+  return false;
+}
+
+// static
+UniquePtr<nsComposeTxtSrvFilter> nsComposeTxtSrvFilter::CreateHelper(
+    bool aIsForMail) {
+  auto filter = MakeUnique<nsComposeTxtSrvFilter>();
+  filter->Init(aIsForMail);
+  return filter;
+}
diff --git a/editor/spellchecker/nsComposeTxtSrvFilter.h b/editor/spellchecker/nsComposeTxtSrvFilter.h
new file mode 100644
index 0000000000..b2de83451b
--- /dev/null
+++ b/editor/spellchecker/nsComposeTxtSrvFilter.h
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; tab-width: 2; 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 nsComposeTxtSrvFilter_h__
+#define nsComposeTxtSrvFilter_h__
+
+#include "mozilla/UniquePtr.h"
+
+class nsINode;
+
+/**
+ * This class enables those using it to skip over certain nodes when
+ * traversing content.
+ *
+ * This filter is used to skip over various form control nodes and
+ * mail's cite nodes
+ */
+class nsComposeTxtSrvFilter final {
+ public:
+  static mozilla::UniquePtr<nsComposeTxtSrvFilter> CreateNormalFilter() {
+    return CreateHelper(false);
+  }
+  static mozilla::UniquePtr<nsComposeTxtSrvFilter> CreateMailFilter() {
+    return CreateHelper(true);
+  }
+
+  /**
+   * Indicates whether the content node should be skipped by the iterator
+   *  @param aNode - node to skip
+   */
+  bool Skip(nsINode* aNode) const;
+
+ private:
+  // Helper - Intializer
+  void Init(bool aIsForMail) { mIsForMail = aIsForMail; }
+
+  static mozilla::UniquePtr<nsComposeTxtSrvFilter> CreateHelper(
+      bool aIsForMail);
+
+  bool mIsForMail = false;
+};
+
+#endif
diff --git a/editor/spellchecker/nsIInlineSpellChecker.idl b/editor/spellchecker/nsIInlineSpellChecker.idl
new file mode 100644
index 0000000000..d6f66a793d
--- /dev/null
+++ b/editor/spellchecker/nsIInlineSpellChecker.idl
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 2; 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 "nsISupports.idl"
+#include "domstubs.idl"
+
+interface nsIEditor;
+interface nsIEditorSpellCheck;
+
+webidl Node;
+webidl Range;
+
+[scriptable, uuid(b7b7a77c-40c4-4196-b0b7-b0338243b3fe)]
+interface nsIInlineSpellChecker : nsISupports
+{
+  readonly attribute nsIEditorSpellCheck spellChecker;
+
+  void init(in nsIEditor aEditor);
+  void cleanup(in boolean aDestroyingFrames);
+
+  attribute boolean enableRealTimeSpell;
+
+  void spellCheckRange(in Range aSelection);
+
+  Range getMisspelledWord(in Node aNode, in unsigned long aOffset);
+  [can_run_script]
+  void replaceWord(in Node aNode,
+                   in unsigned long aOffset,
+                   in AString aNewword);
+  void addWordToDictionary(in AString aWord);
+  void removeWordFromDictionary(in AString aWord);
+
+  void ignoreWord(in AString aWord);
+  void ignoreWords(in Array<AString> aWordsToIgnore);
+  void updateCurrentDictionary();
+
+  readonly attribute boolean spellCheckPending;
+};
diff --git a/editor/spellchecker/tests/bug1200533_subframe.html b/editor/spellchecker/tests/bug1200533_subframe.html
new file mode 100644
index 0000000000..f095c0601f
--- /dev/null
+++ b/editor/spellchecker/tests/bug1200533_subframe.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta http-equiv="Content-Language" content="en-US">
+</head>
+<body>
+<textarea id="none">root en-US</textarea>
+<textarea id="en-GB" lang="en-GB">root en-US, but element en-GB</textarea>
+<textarea id="en-gb" lang="en-gb">root en-US, but element en-gb (lower case)</textarea>
+<textarea id="en-ZA-not-avail" lang="en-ZA">root en-US, but element en-ZA (which is not installed)</textarea>
+<textarea id="en-generic" lang="en">root en-US, but element en</textarea>
+<textarea id="en" lang="en">root en-US, but element en</textarea>
+<textarea id="ko-not-avail" lang="ko">root en-US, but element ko (which is not installed)</textarea>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/bug1204147_subframe.html b/editor/spellchecker/tests/bug1204147_subframe.html
new file mode 100644
index 0000000000..a9b1225cd9
--- /dev/null
+++ b/editor/spellchecker/tests/bug1204147_subframe.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html>
+<head>
+</head>
+<body>
+<textarea id="en-GB" lang="en-GB">element en-GB</textarea>
+<textarea id="en-US" lang="testing-XX">element should default to en-US</textarea>
+
+<div id="trouble-maker" contenteditable>the presence of this div triggers the faulty code path</div>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/bug1204147_subframe2.html b/editor/spellchecker/tests/bug1204147_subframe2.html
new file mode 100644
index 0000000000..935777bd99
--- /dev/null
+++ b/editor/spellchecker/tests/bug1204147_subframe2.html
@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<html>
+<head>
+</head>
+<body>
+<textarea id="en-GB" lang="en-GB">element en-GB</textarea>
+<textarea id="en-US" lang="testing-XX">element should default to en-US</textarea>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/bug678842_subframe.html b/editor/spellchecker/tests/bug678842_subframe.html
new file mode 100644
index 0000000000..39d578ee41
--- /dev/null
+++ b/editor/spellchecker/tests/bug678842_subframe.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html>
+<head>
+</head>
+<body>
+<textarea id="textarea" lang="testing-XXX"></textarea>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/bug717433_subframe.html b/editor/spellchecker/tests/bug717433_subframe.html
new file mode 100644
index 0000000000..3c2927e88f
--- /dev/null
+++ b/editor/spellchecker/tests/bug717433_subframe.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html>
+<head>
+</head>
+<body>
+<textarea id="textarea" lang="en"></textarea>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/chrome.toml b/editor/spellchecker/tests/chrome.toml
new file mode 100644
index 0000000000..f5fbdfac31
--- /dev/null
+++ b/editor/spellchecker/tests/chrome.toml
@@ -0,0 +1,7 @@
+[DEFAULT]
+prefs = ["gfx.font_loader.delay=0"]
+
+skip-if = ["os == 'android'"]
+
+["test_nsIEditorSpellCheck_ReplaceWord.html"]
+support-files = ["spellcheck.js"]
diff --git a/editor/spellchecker/tests/de-DE/de_DE.aff b/editor/spellchecker/tests/de-DE/de_DE.aff
new file mode 100644
index 0000000000..5dc6896b6d
--- /dev/null
+++ b/editor/spellchecker/tests/de-DE/de_DE.aff
@@ -0,0 +1,2 @@
+# Affix file for German English dictionary
+# Fake file, nothing here.
diff --git a/editor/spellchecker/tests/de-DE/de_DE.dic b/editor/spellchecker/tests/de-DE/de_DE.dic
new file mode 100644
index 0000000000..415c216861
--- /dev/null
+++ b/editor/spellchecker/tests/de-DE/de_DE.dic
@@ -0,0 +1,6 @@
+5
+ein
+guter
+heute
+ist
+Tag
diff --git a/editor/spellchecker/tests/en-AU/en_AU.aff b/editor/spellchecker/tests/en-AU/en_AU.aff
new file mode 100644
index 0000000000..e0c467248d
--- /dev/null
+++ b/editor/spellchecker/tests/en-AU/en_AU.aff
@@ -0,0 +1,2 @@
+# Affix file for British English dictionary
+# Fake file, nothing here.
diff --git a/editor/spellchecker/tests/en-AU/en_AU.dic b/editor/spellchecker/tests/en-AU/en_AU.dic
new file mode 100644
index 0000000000..0a1be725d4
--- /dev/null
+++ b/editor/spellchecker/tests/en-AU/en_AU.dic
@@ -0,0 +1,4 @@
+3
+Mary
+Paul
+Peter
diff --git a/editor/spellchecker/tests/en-GB/en_GB.aff b/editor/spellchecker/tests/en-GB/en_GB.aff
new file mode 100644
index 0000000000..e0c467248d
--- /dev/null
+++ b/editor/spellchecker/tests/en-GB/en_GB.aff
@@ -0,0 +1,2 @@
+# Affix file for British English dictionary
+# Fake file, nothing here.
diff --git a/editor/spellchecker/tests/en-GB/en_GB.dic b/editor/spellchecker/tests/en-GB/en_GB.dic
new file mode 100644
index 0000000000..0a1be725d4
--- /dev/null
+++ b/editor/spellchecker/tests/en-GB/en_GB.dic
@@ -0,0 +1,4 @@
+3
+Mary
+Paul
+Peter
diff --git a/editor/spellchecker/tests/mochitest.toml b/editor/spellchecker/tests/mochitest.toml
new file mode 100644
index 0000000000..cd0afc4d9b
--- /dev/null
+++ b/editor/spellchecker/tests/mochitest.toml
@@ -0,0 +1,104 @@
+[DEFAULT]
+prefs = ["gfx.font_loader.delay=0"]
+
+skip-if = ["os == 'android'"]
+support-files = [
+  "en-GB/en_GB.dic",
+  "en-GB/en_GB.aff",
+  "en-AU/en_AU.dic",
+  "en-AU/en_AU.aff",
+  "de-DE/de_DE.dic",
+  "de-DE/de_DE.aff",
+  "ru-RU/ru_RU.dic",
+  "ru-RU/ru_RU.aff",
+  "spellcheck.js",
+]
+
+["test_async_UpdateCurrentDictionary.html"]
+
+["test_bug366682.html"]
+
+["test_bug432225.html"]
+
+["test_bug484181.html"]
+
+["test_bug596333.html"]
+
+["test_bug636465.html"]
+
+["test_bug678842.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+support-files = ["bug678842_subframe.html"]
+
+["test_bug697981.html"]
+
+["test_bug717433.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+support-files = ["bug717433_subframe.html"]
+
+["test_bug1100966.html"]
+
+["test_bug1154791.html"]
+
+["test_bug1200533.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+support-files = ["bug1200533_subframe.html"]
+
+["test_bug1204147.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+support-files = [
+  "bug1204147_subframe.html",
+  "bug1204147_subframe2.html",
+]
+
+["test_bug1205983.html"]
+
+["test_bug1209414.html"]
+
+["test_bug1219928.html"]
+skip-if = ["true"]
+
+["test_bug1365383.html"]
+
+["test_bug1368544.html"]
+
+["test_bug1402822.html"]
+
+["test_bug1418629.html"]
+
+["test_bug1497480.html"]
+
+["test_bug1602526.html"]
+
+["test_bug1761273.html"]
+
+["test_bug1773802.html"]
+
+["test_bug1837268.html"]
+
+["test_multiple_content_languages.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+support-files = ["multiple_content_languages_subframe.html"]
+
+["test_spellcheck_after_edit.html"]
+
+["test_spellcheck_after_pressing_navigation_key.html"]
+
+["test_spellcheck_selection.html"]
+
+["test_suggest.html"]
diff --git a/editor/spellchecker/tests/multiple_content_languages_subframe.html b/editor/spellchecker/tests/multiple_content_languages_subframe.html
new file mode 100644
index 0000000000..da6a4ed664
--- /dev/null
+++ b/editor/spellchecker/tests/multiple_content_languages_subframe.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta http-equiv="Content-Language" content="en-US, en-GB, ko, en-CA">
+</head>
+<body>
+<textarea id="none">root en-US and en-GB</textarea>
+<textarea id="en-GB" lang="en-GB">root multiple, but element only en-GB</textarea>
+<textarea id="en-ZA-not-avail" lang="en-ZA">root multiple en, but element en-ZA (which is not installed)</textarea>
+<textarea id="en" lang="en">root multiple en, but element en</textarea>
+<textarea id="ko-not-avail" lang="ko">root multiple en, but element ko (which is not installed)</textarea>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/ru-RU/ru_RU.aff b/editor/spellchecker/tests/ru-RU/ru_RU.aff
new file mode 100644
index 0000000000..c6cf721484
--- /dev/null
+++ b/editor/spellchecker/tests/ru-RU/ru_RU.aff
@@ -0,0 +1 @@
+SET KOI8-R
diff --git a/editor/spellchecker/tests/ru-RU/ru_RU.dic b/editor/spellchecker/tests/ru-RU/ru_RU.dic
new file mode 100644
index 0000000000..dbfe3a9f23
--- /dev/null
+++ b/editor/spellchecker/tests/ru-RU/ru_RU.dic
@@ -0,0 +1,2 @@
+1
+ÐÒÁ×ÉÌØÎÙÊ
diff --git a/editor/spellchecker/tests/spellcheck.js b/editor/spellchecker/tests/spellcheck.js
new file mode 100644
index 0000000000..b6a1586628
--- /dev/null
+++ b/editor/spellchecker/tests/spellcheck.js
@@ -0,0 +1,36 @@
+function isSpellingCheckOk(aEditor, aMisspelledWords, aTodo = false) {
+  var selcon = aEditor.selectionController;
+  var sel = selcon.getSelection(selcon.SELECTION_SPELLCHECK);
+  var numWords = sel.rangeCount;
+
+  if (aTodo) {
+    todo_is(
+      numWords,
+      aMisspelledWords.length,
+      "Correct number of misspellings and words."
+    );
+  } else {
+    is(
+      numWords,
+      aMisspelledWords.length,
+      "Correct number of misspellings and words."
+    );
+  }
+
+  if (numWords !== aMisspelledWords.length) {
+    return false;
+  }
+
+  for (var i = 0; i < numWords; ++i) {
+    var word = String(sel.getRangeAt(i));
+    if (aTodo) {
+      todo_is(word, aMisspelledWords[i], "Misspelling is what we think it is.");
+    } else {
+      is(word, aMisspelledWords[i], "Misspelling is what we think it is.");
+    }
+    if (word !== aMisspelledWords[i]) {
+      return false;
+    }
+  }
+  return true;
+}
diff --git a/editor/spellchecker/tests/test_async_UpdateCurrentDictionary.html b/editor/spellchecker/tests/test_async_UpdateCurrentDictionary.html
new file mode 100644
index 0000000000..d586eef721
--- /dev/null
+++ b/editor/spellchecker/tests/test_async_UpdateCurrentDictionary.html
@@ -0,0 +1,60 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=856270
+-->
+<head>
+  <title>Test for Bug 856270 - Async UpdateCurrentDictionary</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=856270">Mozilla Bug 856270</a>
+<p id="display"></p>
+<div id="content">
+<textarea id="editor" spellcheck="true"></textarea>
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(start);
+
+function start() {
+  var textarea = document.getElementById("editor");
+  textarea.focus();
+
+  const { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  )
+  onSpellCheck(textarea, function() {
+    var isc = SpecialPowers.wrap(textarea).editor.getInlineSpellChecker(false);
+    ok(isc, "Inline spell checker should exist after focus and spell check");
+    var sc = isc.spellChecker;
+
+    sc.setCurrentDictionaries(["testing-XX"]).then(() => {
+      is(true, false, "Setting a non-existent dictionary should fail");
+    }, () => {
+      let currentDictionaries = sc.getCurrentDictionaries();
+
+      is(currentDictionaries.length, 0, "expected no dictionaries");
+      // First, set the lang attribute on the textarea, call Update, and make
+      // sure the spell checker's language was updated appropriately.
+      var lang = "en-US";
+      textarea.setAttribute("lang", lang);
+      sc.UpdateCurrentDictionary(function() {
+        currentDictionaries = sc.getCurrentDictionaries();
+        is(currentDictionaries.length, 1, "expected one dictionary");
+        is(sc.getCurrentDictionaries()[0], lang,
+          "UpdateCurrentDictionary should set the current dictionary.");
+        sc.setCurrentDictionaries([]).then(() => {
+          SimpleTest.finish();
+        });
+      });
+    });
+  });
+}
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1100966.html b/editor/spellchecker/tests/test_bug1100966.html
new file mode 100644
index 0000000000..15f1e03a3b
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1100966.html
@@ -0,0 +1,74 @@
+<!DOCTYPE>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1100966
+-->
+<head>
+  <title>Test for Bug 1100966</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+</head>
+<body>
+<div id="display">
+</div>
+<div id="content" contenteditable>
+=====<br>
+correct<br>
+fivee sixx<br>
+====
+</div>
+<pre id="test">
+</pre>
+
+<script class="testbody" type="application/javascript">
+
+let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+/** Test for Bug 1100966 **/
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(function() {
+  var div = document.getElementById("content");
+  div.focus();
+  synthesizeMouseAtCenter(div, {});
+
+  getSpellChecker().UpdateCurrentDictionary(() => {
+    sendString(" ");
+    SimpleTest.executeSoon(function() {
+      sendString("a");
+      SimpleTest.executeSoon(function() {
+        synthesizeKey("KEY_Backspace");
+
+        maybeOnSpellCheck(div, function() {
+          var sel = getSpellCheckSelection();
+          is(sel.rangeCount, 2, "We should have two misspelled words");
+          is(String(sel.getRangeAt(0)), "fivee", "Correct misspelled word");
+          is(String(sel.getRangeAt(1)), "sixx", "Correct misspelled word");
+
+          SimpleTest.finish();
+        });
+      });
+    });
+  });
+});
+
+function getEditor() {
+  var editingSession = SpecialPowers.wrap(window).docShell.editingSession;
+  return editingSession.getEditorForWindow(window);
+}
+
+function getSpellChecker() {
+  return getEditor().getInlineSpellChecker(false).spellChecker;
+}
+
+function getSpellCheckSelection() {
+  var selcon = getEditor().selectionController;
+  return selcon.getSelection(selcon.SELECTION_SPELLCHECK);
+}
+
+</script>
+</body>
+
+</html>
diff --git a/editor/spellchecker/tests/test_bug1154791.html b/editor/spellchecker/tests/test_bug1154791.html
new file mode 100644
index 0000000000..1552c7eff8
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1154791.html
@@ -0,0 +1,74 @@
+<!DOCTYPE>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1154791
+-->
+<head>
+  <title>Test for Bug 1154791</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+</head>
+<body>
+<div id="display">
+</div>
+
+<div id="content" contenteditable>
+<tt>thiss onee is stilll a</tt>
+</div>
+
+<pre id="test">
+</pre>
+
+<script class="testbody" type="application/javascript">
+
+let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+/** Test for Bug 1154791 **/
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(function() {
+  var div = document.getElementById("content");
+  div.focus();
+  getSpellChecker().UpdateCurrentDictionary(() => {
+    synthesizeMouseAtCenter(div, {});
+    synthesizeKey("KEY_ArrowLeft");
+    synthesizeKey("KEY_ArrowLeft");
+
+    SimpleTest.executeSoon(function() {
+      synthesizeKey("KEY_Backspace");
+      SimpleTest.executeSoon(function() {
+        sendString(" ");
+
+        maybeOnSpellCheck(div, function() {
+          var sel = getSpellCheckSelection();
+          is(sel.rangeCount, 2, "We should have two misspelled words");
+          is(String(sel.getRangeAt(0)), "thiss", "Correct misspelled word");
+          is(String(sel.getRangeAt(1)), "onee", "Correct misspelled word");
+
+          SimpleTest.finish();
+        });
+      });
+    });
+  });
+});
+
+function getEditor() {
+  var editingSession = SpecialPowers.wrap(window).docShell.editingSession;
+  return editingSession.getEditorForWindow(window);
+}
+
+function getSpellChecker() {
+  return getEditor().getInlineSpellChecker(false).spellChecker;
+}
+
+function getSpellCheckSelection() {
+  var selcon = getEditor().selectionController;
+  return selcon.getSelection(selcon.SELECTION_SPELLCHECK);
+}
+
+</script>
+</body>
+
+</html>
diff --git a/editor/spellchecker/tests/test_bug1200533.html b/editor/spellchecker/tests/test_bug1200533.html
new file mode 100644
index 0000000000..0f75825013
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1200533.html
@@ -0,0 +1,163 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1200533
+-->
+<head>
+  <title>Test for Bug 1200533</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1200533">Mozilla Bug 1200533</a>
+<p id="display"></p>
+<iframe id="content"></iframe>
+
+</div>
+<pre id="test">
+<script class="testbody" ttype="application/javascript">
+
+/** Test for Bug 1200533 **/
+/** Visit the elements defined above and check the dictionary we got **/
+SimpleTest.waitForExplicitFinish();
+var content = document.getElementById("content");
+
+var tests = [
+    // text area, value of spellchecker.dictionary, result.
+    // Result: Document language.
+    [ "none",  "", "en-US" ],
+    // Result: Element language.
+    [ "en-GB", "", "en-GB" ],
+    [ "en-gb", "", "en-GB" ],
+    // Result: Random en-* or en-US (if application locale is en-US).
+    [ "en-ZA-not-avail", "", "*" ],
+    [ "en-generic",      "", "*" ],
+    [ "en",              "", "*" ],
+    // Result: Locale.
+    [ "ko-not-avail",    "", "en-US" ],
+
+    // Result: Preference value in all cases.
+    [ "en-ZA-not-avail", "en-AU", "en-AU" ],
+    [ "en-generic",      "en-AU", "en-AU" ],
+    [ "ko-not-avail",    "en-AU", "en-AU" ],
+
+    // Result: Random en-*.
+    [ "en-ZA-not-avail", "de-DE", "*" ],
+    [ "en-generic",      "de-DE", "*" ],
+    // Result: Preference value.
+    [ "ko-not-avail",    "de-DE", "de-DE" ],
+  ];
+
+var loadCount = 0;
+var retrying = false;
+var script;
+
+var loadListener = async function(evt) {
+  if (loadCount == 0) {
+    script = SpecialPowers.loadChromeScript(function() {
+      /* eslint-env mozilla/chrome-script */
+      // eslint-disable-next-line mozilla/use-services
+      var dir = Cc["@mozilla.org/file/directory_service;1"]
+                  .getService(Ci.nsIProperties)
+                  .get("CurWorkD", Ci.nsIFile);
+      dir.append("tests");
+      dir.append("editor");
+      dir.append("spellchecker");
+      dir.append("tests");
+
+      var hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                       .getService(Ci.mozISpellCheckingEngine);
+
+      // Install en-GB, en-AU and de-DE dictionaries.
+      var en_GB = dir.clone();
+      var en_AU = dir.clone();
+      var de_DE = dir.clone();
+      en_GB.append("en-GB");
+      en_AU.append("en-AU");
+      de_DE.append("de-DE");
+      hunspell.addDirectory(en_GB);
+      hunspell.addDirectory(en_AU);
+      hunspell.addDirectory(de_DE);
+
+      addMessageListener("check-existence",
+                         () => [en_GB.exists(), en_AU.exists(),
+                                de_DE.exists()]);
+      addMessageListener("destroy", () => {
+        hunspell.removeDirectory(en_GB);
+        hunspell.removeDirectory(en_AU);
+        hunspell.removeDirectory(de_DE);
+      });
+    });
+    var existenceChecks = await script.sendQuery("check-existence");
+    is(existenceChecks[0], true, "true expected (en-GB directory should exist)");
+    is(existenceChecks[1], true, "true expected (en-AU directory should exist)");
+    is(existenceChecks[2], true, "true expected (de-DE directory should exist)");
+  }
+
+  SpecialPowers.pushPrefEnv({set: [["spellchecker.dictionary", tests[loadCount][1]]]},
+                            function() { continueTest(evt); });
+};
+
+function continueTest(evt) {
+  var doc = evt.target.contentDocument;
+  var elem = doc.getElementById(tests[loadCount][0]);
+  var editor = SpecialPowers.wrap(elem).editor;
+  editor.setSpellcheckUserOverride(true);
+  var inlineSpellChecker = editor.getInlineSpellChecker(true);
+  const is_en_US = SpecialPowers.Services.locale.appLocaleAsBCP47 == "en-US";
+
+  const { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  onSpellCheck(elem, async function() {
+    var spellchecker = inlineSpellChecker.spellChecker;
+    let currentDictionaries;
+    try {
+      currentDictionaries = spellchecker.getCurrentDictionaries();
+    } catch (e) {}
+
+    if (!currentDictionaries && !retrying) {
+      // It's possible for an asynchronous font-list update to cause a reflow
+      // that disrupts the async spell-check and results in not getting a
+      // current dictionary here; if that happens, we retry the same testcase
+      // by reloading the iframe without bumping loadCount.
+      info(`No current dictionary: retrying testcase ${loadCount}`);
+      retrying = true;
+    } else {
+      is(currentDictionaries.length, 1, "expected one dictionary");
+      let dict = currentDictionaries[0];
+      if (tests[loadCount][2] != "*") {
+        is(dict, tests[loadCount][2], "expected " + tests[loadCount][2]);
+      } else if (is_en_US && tests[loadCount][0].startsWith("en")) {
+        // Current application locale is en-US and content lang is en or
+        // en-unknown, so we should use en-US dictionary as default.
+        is(dict, "en-US", "expected en-US that is application locale");
+      } else {
+        var gotEn = (dict == "en-GB" || dict == "en-AU" || dict == "en-US");
+        is(gotEn, true, "expected en-AU or en-GB or en-US");
+      }
+
+      loadCount++;
+      retrying = false;
+    }
+
+    if (loadCount < tests.length) {
+      // Load the iframe again.
+      content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/bug1200533_subframe.html?firstload=false";
+    } else {
+      // Remove the fake  dictionaries again, since it's otherwise picked up by later tests.
+      await script.sendQuery("destroy");
+
+      SimpleTest.finish();
+    }
+  });
+}
+
+content.addEventListener("load", loadListener);
+
+content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/bug1200533_subframe.html?firstload=true";
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1204147.html b/editor/spellchecker/tests/test_bug1204147.html
new file mode 100644
index 0000000000..39935c0d5c
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1204147.html
@@ -0,0 +1,115 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1204147
+-->
+<head>
+  <title>Test for Bug 1204147</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1204147">Mozilla Bug 1204147</a>
+<p id="display"></p>
+<iframe id="content"></iframe>
+</div>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+/** Test for Bug 1204147 **/
+SimpleTest.waitForExplicitFinish();
+var content = document.getElementById("content");
+// Load a subframe containing an editor with using "en-GB". At first
+// load, it will set the dictionary to "en-GB". The bug was that a content preference
+// was also created. At second load, we check the dictionary for another element,
+// one that should use "en-US". With the bug corrected, we get "en-US", before
+// we got "en-GB" from the content preference.
+
+var firstLoad = true;
+var script;
+
+var loadListener = async function(evt) {
+  if (firstLoad) {
+    script = SpecialPowers.loadChromeScript(function() {
+      /* eslint-env mozilla/chrome-script */
+      // eslint-disable-next-line mozilla/use-services
+      var dir = Cc["@mozilla.org/file/directory_service;1"]
+                  .getService(Ci.nsIProperties)
+                  .get("CurWorkD", Ci.nsIFile);
+      dir.append("tests");
+      dir.append("editor");
+      dir.append("spellchecker");
+      dir.append("tests");
+
+      var hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                       .getService(Ci.mozISpellCheckingEngine);
+
+      // Install en-GB dictionary.
+      let en_GB = dir.clone();
+      en_GB.append("en-GB");
+      hunspell.addDirectory(en_GB);
+
+      addMessageListener("en_GB-exists", () => en_GB.exists());
+      addMessageListener("destroy", () => hunspell.removeDirectory(en_GB));
+    });
+    is(await script.sendQuery("en_GB-exists"), true,
+       "true expected (en-GB directory should exist)");
+  }
+
+  var doc = evt.target.contentDocument;
+  var elem;
+  if (firstLoad) {
+    elem = doc.getElementById("en-GB");
+  } else {
+    elem = doc.getElementById("en-US");
+  }
+
+  var editor = SpecialPowers.wrap(elem).editor;
+  editor.setSpellcheckUserOverride(true);
+  var inlineSpellChecker = editor.getInlineSpellChecker(true);
+
+  const { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  onSpellCheck(elem, async function() {
+    let spellchecker = inlineSpellChecker.spellChecker;
+    let currentDictionaries = spellchecker.getCurrentDictionaries();
+    is(currentDictionaries.length, 1, "expected one dictionary");
+    let currentDictionary = currentDictionaries[0];
+    if (firstLoad) {
+      firstLoad = false;
+
+       // First time around, the element's language should be used.
+      is(currentDictionary, "en-GB", "unexpected lang " + currentDictionary + " instead of en-GB");
+
+      // Note that on second load, we load a different page, which does NOT have the trouble-causing
+      // contenteditable in it. Sadly, loading the same page with the trouble-maker in it
+      // doesn't allow the retrieval of the spell check dictionary used for the element,
+      // because the trouble-maker causes the 'global' spell check dictionary to be set to "en-GB"
+      // (since it picks the first one from the list) before we have the chance to retrieve
+      // the dictionary for the element (which happens asynchonously after the spell check has completed).
+      content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/bug1204147_subframe2.html?firstload=false";
+    } else {
+      // Second time around, the element should default to en-US.
+      // Without the fix, the first run sets the content preference to en-GB for the whole site.
+      is(currentDictionary, "en-US", "unexpected lang " + currentDictionary + " instead of en-US");
+      content.removeEventListener("load", loadListener);
+
+      // Remove the fake en-GB dictionary again, since it's otherwise picked up by later tests.
+      await script.sendQuery("destroy");
+
+      // Reset the preference, so the last value we set doesn't collide with the next test.
+      SimpleTest.finish();
+    }
+  });
+};
+
+content.addEventListener("load", loadListener);
+
+content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/bug1204147_subframe.html?firstload=true";
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1205983.html b/editor/spellchecker/tests/test_bug1205983.html
new file mode 100644
index 0000000000..052f46d312
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1205983.html
@@ -0,0 +1,134 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1205983
+-->
+<head>
+  <title>Test for Bug 1205983</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1205983">Mozilla Bug 1205983</a>
+<p id="display"></p>
+</div>
+
+<div contenteditable id="de-DE" lang="de-DE" onfocus="deFocus()">German heute ist ein guter Tag</div>
+<textarea id="en-US" lang="en-US" onfocus="enFocus()">Nogoodword today is a nice day</textarea>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+function getMisspelledWords(editor) {
+  return editor.selectionController.getSelection(SpecialPowers.Ci.nsISelectionController.SELECTION_SPELLCHECK).toString();
+}
+
+var elem_de;
+var editor_de;
+var selcon_de;
+var script;
+
+var { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+/** Test for Bug 1205983 **/
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(async function() {
+  script = SpecialPowers.loadChromeScript(function() {
+    /* eslint-env mozilla/chrome-script */
+    // eslint-disable-next-line mozilla/use-services
+    var dir = Cc["@mozilla.org/file/directory_service;1"]
+                .getService(Ci.nsIProperties)
+                .get("CurWorkD", Ci.nsIFile);
+    dir.append("tests");
+    dir.append("editor");
+    dir.append("spellchecker");
+    dir.append("tests");
+
+    var hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                     .getService(Ci.mozISpellCheckingEngine);
+
+    // Install de-DE dictionary.
+    var de_DE = dir.clone();
+    de_DE.append("de-DE");
+    hunspell.addDirectory(de_DE);
+
+    addMessageListener("de_DE-exists", () => de_DE.exists());
+    addMessageListener("destroy", () => hunspell.removeDirectory(de_DE));
+  });
+  is(await script.sendQuery("de_DE-exists"), true,
+     "true expected (de_DE directory should exist)");
+
+  document.getElementById("de-DE").focus();
+});
+
+function deFocus() {
+  elem_de = document.getElementById("de-DE");
+
+  maybeOnSpellCheck(elem_de, function() {
+    var editingSession = SpecialPowers.wrap(window).docShell.editingSession;
+    editor_de = editingSession.getEditorForWindow(window);
+    selcon_de = editor_de.selectionController;
+    var sel = selcon_de.getSelection(selcon_de.SELECTION_SPELLCHECK);
+
+    // Check that we spelled in German, so there is only one misspelled word.
+    is(sel.toString(), "German", "one misspelled word expected: German");
+
+    // Now focus the textarea, which requires English spelling.
+    document.getElementById("en-US").focus();
+  });
+}
+
+function enFocus() {
+  var elem_en = document.getElementById("en-US");
+  var editor_en =
+    SpecialPowers.wrap(elem_en)
+                 .editor;
+  editor_en.setSpellcheckUserOverride(true);
+  var inlineSpellChecker = editor_en.getInlineSpellChecker(true);
+
+  maybeOnSpellCheck(elem_en, async function() {
+    var spellchecker = inlineSpellChecker.spellChecker;
+    let currentDictionaries = spellchecker.getCurrentDictionaries();
+    is(currentDictionaries.length, 1, "expected one dictionary");
+    let currentDictionary = currentDictionaries[0];
+
+    // Check that the English dictionary is loaded and that the spell check has worked.
+    is(currentDictionary, "en-US", "expected en-US");
+    is(getMisspelledWords(editor_en), "Nogoodword", "one misspelled word expected: Nogoodword");
+
+    // So far all was boring. The important thing is whether the spell check result
+    // in the de-DE editor is still the same. After losing focus, no spell check
+    // updates should take place there.
+    var sel = selcon_de.getSelection(selcon_de.SELECTION_SPELLCHECK);
+    is(sel.toString(), "German", "one misspelled word expected: German");
+
+    // Remove the fake de_DE dictionary again.
+    await script.sendQuery("destroy");
+
+    // Focus again, so the spelling gets updated, but before we need to kill the focus handler.
+    elem_de.onfocus = null;
+    elem_de.blur();
+    elem_de.focus();
+
+    // After removal, the de_DE editor should refresh the spelling with en-US.
+    maybeOnSpellCheck(elem_de, function() {
+      var endSel = selcon_de.getSelection(selcon_de.SELECTION_SPELLCHECK);
+      // eslint-disable-next-line no-useless-concat
+      is(endSel.toString(), "heute" + "ist" + "ein" + "guter",
+         "some misspelled words expected: heute ist ein guter");
+
+      // If we don't reset this, we cause massive leaks.
+      selcon_de = null;
+      editor_de = null;
+
+      SimpleTest.finish();
+    });
+  });
+}
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1209414.html b/editor/spellchecker/tests/test_bug1209414.html
new file mode 100644
index 0000000000..1f266758c2
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1209414.html
@@ -0,0 +1,144 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1209414
+-->
+<head>
+  <title>Test for Bug 1209414</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1209414">Mozilla Bug 1209414</a>
+<p id="display"></p>
+</div>
+
+<textarea id="de-DE" lang="de-DE">heute ist ein guter Tag - today is a good day</textarea>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+const Ci = SpecialPowers.Ci;
+
+function getMisspelledWords(editor) {
+  return editor.selectionController.getSelection(Ci.nsISelectionController.SELECTION_SPELLCHECK).toString();
+}
+
+var elem_de;
+var editor_de;
+var script;
+
+/** Test for Bug 1209414 **/
+/*
+ * All we want to do in this test is change the spelling using a right-click and selection from the menu.
+ * This is necessary since all the other tests use setCurrentDictionaries() which doesn't reflect
+ * user behaviour.
+ */
+
+let { maybeOnSpellCheck, onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(async function() {
+  script = SpecialPowers.loadChromeScript(function() {
+    /* eslint-env mozilla/chrome-script */
+    var chromeWin = actorParent.rootFrameLoader
+                    .ownerElement.ownerGlobal.browsingContext.topChromeWindow;
+    var contextMenu = chromeWin.document.getElementById("contentAreaContextMenu");
+    contextMenu.addEventListener("popupshown",
+                                 () => sendAsyncMessage("popupshown"));
+
+    // eslint-disable-next-line mozilla/use-services
+    var dir = Cc["@mozilla.org/file/directory_service;1"]
+                .getService(Ci.nsIProperties)
+                .get("CurWorkD", Ci.nsIFile);
+    dir.append("tests");
+    dir.append("editor");
+    dir.append("spellchecker");
+    dir.append("tests");
+
+    var hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                     .getService(Ci.mozISpellCheckingEngine);
+
+    // Install de-DE dictionary.
+    let de_DE = dir.clone();
+    de_DE.append("de-DE");
+    hunspell.addDirectory(de_DE);
+
+    addMessageListener("hidepopup", function() {
+      var state = contextMenu.state;
+
+      // Select Language from the menu.  Take a look at
+      // toolkit/modules/InlineSpellChecker.sys.mjs to see how the menu works.
+      contextMenu.ownerDocument.getElementById("spell-check-dictionary-en-US")
+                 .doCommand();
+      contextMenu.hidePopup();
+      return state;
+    });
+    addMessageListener("destroy", () => hunspell.removeDirectory(de_DE));
+    addMessageListener("contextMenu-not-null", () => contextMenu != null);
+    addMessageListener("de_DE-exists", () => de_DE.exists());
+  });
+  is(await script.sendQuery("contextMenu-not-null"), true,
+     "Got context menu XUL");
+  is(await script.sendQuery("de_DE-exists"), true,
+     "true expected (de_DE directory should exist)");
+  script.addMessageListener("popupshown", handlePopup);
+
+  elem_de = document.getElementById("de-DE");
+  editor_de = SpecialPowers.wrap(elem_de).editor;
+  editor_de.setSpellcheckUserOverride(true);
+
+  maybeOnSpellCheck(elem_de, function() {
+    var inlineSpellChecker = editor_de.getInlineSpellChecker(true);
+    var spellchecker = inlineSpellChecker.spellChecker;
+    let currentDictionaries = spellchecker.getCurrentDictionaries();
+
+    // Check that the German dictionary is loaded and that the spell check has worked.
+    is(currentDictionaries.length, 1, "expected one dictionary");
+    is(currentDictionaries[0], "de-DE", "expected de-DE");
+    // eslint-disable-next-line no-useless-concat
+    is(getMisspelledWords(editor_de), "today" + "is" + "a" + "good" + "day", "some misspelled words expected: today is a good day");
+
+    // Focus again, just to be sure that the context-click won't trigger another spell check.
+    elem_de.focus();
+
+    // Make sure all spell checking action is done before right-click to select the en-US dictionary.
+    maybeOnSpellCheck(elem_de, function() {
+      synthesizeMouse(elem_de, 2, 2, { type: "contextmenu", button: 2 }, window);
+    });
+  });
+});
+
+async function handlePopup() {
+  var state = await script.sendQuery("hidepopup");
+  is(state, "open", "checking if popup is open");
+
+  onSpellCheck(elem_de, async function() {
+    var inlineSpellChecker = editor_de.getInlineSpellChecker(true);
+    var spellchecker = inlineSpellChecker.spellChecker;
+    let currentDictionaries = spellchecker.getCurrentDictionaries();
+
+    // Check that the English dictionary is loaded and that the spell check has worked.
+    is(currentDictionaries.length, 2, "expected two dictionaries");
+    let dictionaryArray = Array.from(currentDictionaries);
+    ok(dictionaryArray.includes("de-DE"), "expected de-DE");
+    ok(dictionaryArray.includes("en-US"), "expected en-US");
+    is(getMisspelledWords(editor_de), "", "No misspelled words expected");
+
+    // Remove the fake de_DE dictionary again.
+    await script.sendQuery("destroy");
+
+    // This will clear the content preferences and reset "spellchecker.dictionary".
+    spellchecker.setCurrentDictionaries([]).then(() => {
+      SimpleTest.finish();
+    });
+  });
+}
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1219928.html b/editor/spellchecker/tests/test_bug1219928.html
new file mode 100644
index 0000000000..0636b981df
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1219928.html
@@ -0,0 +1,69 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1219928
+-->
+<head>
+  <title>Test for Bug 1219928</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1219928">Mozilla Bug 1219928</a>
+<p id="display"></p>
+
+<div contenteditable id="en-US" lang="en-US">
+<p>And here a missspelled word</p>
+<style>
+<!-- and here another onnee in a style comment -->
+</style>
+</div>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+/** Test for Bug 1219928 **/
+/* Very simple test to check that <style> blocks are skipped in the spell check */
+
+var spellchecker;
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(function() {
+  var { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+
+  var elem = document.getElementById("en-US");
+  elem.focus();
+
+  maybeOnSpellCheck(elem, function() {
+    var editingSession = SpecialPowers.wrap(window).docShell.editingSession;
+    var editor = editingSession.getEditorForWindow(window);
+    var selcon = editor.selectionController;
+    var sel = selcon.getSelection(selcon.SELECTION_SPELLCHECK);
+
+    is(sel.toString(), "missspelled", "one misspelled word expected: missspelled");
+
+    spellchecker = SpecialPowers.Cu.createSpellChecker();
+    spellchecker.setFilterType(spellchecker.FILTERTYPE_NORMAL);
+    spellchecker.InitSpellChecker(editor, false, spellCheckStarted);
+  });
+});
+
+function spellCheckStarted() {
+  var misspelledWord = spellchecker.GetNextMisspelledWord();
+  is(misspelledWord, "missspelled", "first misspelled word expected: missspelled");
+
+  // Without the fix, the next misspelled word was 'onnee', so we check that we don't get it.
+  misspelledWord = spellchecker.GetNextMisspelledWord();
+  isnot(misspelledWord, "onnee", "second misspelled word should not be: onnee");
+
+  spellchecker = "";
+
+  SimpleTest.finish();
+}
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1365383.html b/editor/spellchecker/tests/test_bug1365383.html
new file mode 100644
index 0000000000..a4b71d15bb
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1365383.html
@@ -0,0 +1,46 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1365383
+-->
+<head>
+  <title>Test for Bug 1365383</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1365383">Mozilla Bug 1365383</a>
+<p id="display"></p>
+<div id="content">
+<textarea id="editor" spellcheck="true"></textarea>
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(() => {
+  let textarea = document.getElementById("editor");
+  let editor = SpecialPowers.wrap(textarea).editor;
+
+  let spellChecker = SpecialPowers.Cu.createSpellChecker();
+
+  // Callback parameter isn't set
+  spellChecker.InitSpellChecker(editor, false);
+
+  textarea.focus();
+
+  const { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  onSpellCheck(textarea, () => {
+    // Callback parameter isn't set
+    spellChecker.UpdateCurrentDictionary();
+
+    var canSpellCheck = spellChecker.canSpellCheck();
+    ok(canSpellCheck, "spellCheck is enabled");
+    SimpleTest.finish();
+  });
+});
+</script>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1368544.html b/editor/spellchecker/tests/test_bug1368544.html
new file mode 100644
index 0000000000..577e90635f
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1368544.html
@@ -0,0 +1,91 @@
+<!DOCTYPE html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi=id=1368544
+-->
+<html>
+<head>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1368544">Mozilla Bug 1368544</a>
+<div id="display"></div>
+<textarea id=textarea></textarea>
+<pre id="test">
+</pre>
+
+<script class="testbody">
+function hasEmptyTextNode(div) {
+  return div.firstChild.nodeType === Node.TEXT_NODE && div.firstChild.length === 0;
+}
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(() => {
+  let textarea = document.getElementById("textarea");
+  let editor = SpecialPowers.wrap(textarea).editor;
+
+  let spellChecker = SpecialPowers.Cu.createSpellChecker();
+  spellChecker.InitSpellChecker(editor, false);
+
+  textarea.focus();
+
+  const { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  onSpellCheck(textarea, () => {
+    spellChecker.UpdateCurrentDictionary(() => {
+      textarea.value = "ABC";
+      ok(editor.rootElement.hasChildNodes(),
+         "editor of textarea has child nodes");
+      sendString("D");
+      is(textarea.value, "ABCD", "D is last character");
+      ok(editor.rootElement.hasChildNodes(),
+         "editor of textarea has child nodes");
+      textarea.value = "";
+      ok(editor.rootElement.hasChildNodes(),
+         "editor of textarea has child node even if value is empty");
+
+      sendString("AAA");
+      synthesizeKey("KEY_Backspace", {repeat: 3});
+      is(textarea.value, "", "value is empty");
+      ok(editor.rootElement.hasChildNodes(),
+         "editor of textarea has child node even if value is empty");
+
+      textarea.value = "ABC";
+      SpecialPowers.wrap(textarea).setUserInput("");
+      is(textarea.value, "",
+         "textarea should become empty when setUserInput() is called with empty string");
+      ok(hasEmptyTextNode(editor.rootElement),
+            "editor of textarea should only have an empty text node when user input emulation set the value to empty");
+      todo(editor.rootElement.childNodes.length === 1, "editor of textarea should only have a single child");
+      if (editor.rootElement.childNodes.length > 1) {
+        is(editor.rootElement.childNodes.length, 2, "There should be only one additional <br> node");
+        is(editor.rootElement.lastChild.tagName.toLowerCase(), "br", "The node should be a <br> element node");
+        ok(!SpecialPowers.wrap(editor.rootElement.lastChild).isPaddingForEmptyEditor,
+            "The <br> should not be a padding <br> element");
+      }
+      textarea.value = "ABC";
+      synthesizeKey("KEY_Enter", {repeat: 2});
+      textarea.value = "";
+      ok(editor.rootElement.hasChildNodes(),
+         "editor of textarea has child node even if value is empty");
+
+      sendString("AAA");
+      is(textarea.value, "AAA", "value is AAA");
+      textarea.addEventListener("keyup", (e) => {
+        if (e.key == "Enter") {
+          textarea.value = "";
+          ok(editor.rootElement.hasChildNodes(),
+             "editor of textarea has child node even if value is empty");
+          SimpleTest.finish();
+        }
+      });
+
+      synthesizeKey("KEY_Enter");
+    });
+ });
+});
+</script>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1402822.html b/editor/spellchecker/tests/test_bug1402822.html
new file mode 100644
index 0000000000..505bca6dbb
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1402822.html
@@ -0,0 +1,114 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1402822
+-->
+<head>
+  <title>Test for Bug 1402822</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1402822">Mozilla Bug 1402822</a>
+<p id="display"></p>
+</div>
+
+<textarea id="editor">heute ist ein guter Tag - today is a good day</textarea>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+const Ci = SpecialPowers.Ci;
+
+let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+function getMisspelledWords(editor) {
+  return editor.selectionController.getSelection(Ci.nsISelectionController.SELECTION_SPELLCHECK).toString();
+}
+
+/** Test for Bug 1402822 **/
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(start);
+async function start() {
+  let script = SpecialPowers.loadChromeScript(() => {
+    /* eslint-env mozilla/chrome-script */
+    // eslint-disable-next-line mozilla/use-services
+    let dir = Cc["@mozilla.org/file/directory_service;1"]
+                .getService(Ci.nsIProperties)
+                .get("CurWorkD", Ci.nsIFile);
+    dir.append("tests");
+    dir.append("editor");
+    dir.append("spellchecker");
+    dir.append("tests");
+
+    let hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                     .getService(Ci.mozISpellCheckingEngine);
+
+    // Install de-DE dictionary.
+    let de_DE = dir.clone();
+    de_DE.append("de-DE");
+    hunspell.addDirectory(de_DE);
+
+    addMessageListener("destroy", () => hunspell.removeDirectory(de_DE));
+    addMessageListener("de_DE-exists", () => de_DE.exists());
+  });
+  is(await script.sendQuery("de_DE-exists"), true,
+     "true expected (de_DE directory should exist)");
+
+  let textarea = document.getElementById("editor");
+  let editor = SpecialPowers.wrap(textarea).editor;
+  textarea.focus();
+
+  maybeOnSpellCheck(textarea, () => {
+    let isc = SpecialPowers.wrap(textarea).editor.getInlineSpellChecker(false);
+    ok(isc, "Inline spell checker should exist after focus and spell check");
+    let spellchecker = isc.spellChecker;
+
+    spellchecker.setCurrentDictionaries(["en-US"]).then(() => {
+      let currentDictionaries = spellchecker.getCurrentDictionaries();
+
+      is(currentDictionaries.length, 1, "expected one dictionary");
+      is(currentDictionaries[0], "en-US", "expected en-US");
+      is(getMisspelledWords(editor), "heuteisteinguter", "some misspelled words expected: heuteisteinguter");
+      spellchecker.setCurrentDictionaries(["en-US", "de-DE"]).then(() => {
+        textarea.blur();
+        textarea.focus();
+        maybeOnSpellCheck(textarea, () => {
+          currentDictionaries = spellchecker.getCurrentDictionaries();
+
+          is(currentDictionaries.length, 2, "expected two dictionaries");
+          is(currentDictionaries[0], "en-US", "expected en-US");
+          is(currentDictionaries[1], "de-DE", "expected de-DE");
+          is(getMisspelledWords(editor), "", "No misspelled words expected");
+
+          spellchecker.setCurrentDictionaries(["de-DE"]).then(() => {
+            textarea.blur();
+            textarea.focus();
+            maybeOnSpellCheck(textarea, async function() {
+              currentDictionaries = spellchecker.getCurrentDictionaries();
+
+              is(currentDictionaries.length, 1, "expected one dictionary");
+              is(currentDictionaries[0], "de-DE", "expected de-DE");
+              is(getMisspelledWords(editor), "todayisagoodday", "some misspelled words expected: todayisagoodday");
+
+              // Remove the fake de_DE dictionary again.
+              await script.sendQuery("destroy");
+
+              // This will clear the content preferences and reset "spellchecker.dictionary".
+              spellchecker.setCurrentDictionaries([]).then(() => {
+                SimpleTest.finish();
+              });
+            });
+          });
+        });
+      });
+    });
+  });
+}
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1418629.html b/editor/spellchecker/tests/test_bug1418629.html
new file mode 100644
index 0000000000..3f2c906913
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1418629.html
@@ -0,0 +1,210 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Mozilla bug 1418629</title>
+  <link rel=stylesheet href="/tests/SimpleTest/test.css">
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/editor/spellchecker/tests/spellcheck.js"></script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1418629">Mozilla Bug 1418629</a>
+<p id="display"></p>
+<div id="content" style="display: none;">
+
+</div>
+
+<input id="input1" spellcheck="true">
+<textarea id="textarea1"></textarea>
+<div id="edit1" contenteditable=true></div>
+
+<script>
+const { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+SimpleTest.waitForExplicitFinish();
+
+function getEditor(input) {
+  if (input instanceof HTMLInputElement ||
+      input instanceof HTMLTextAreaElement) {
+    return SpecialPowers.wrap(input).editor;
+  }
+
+  return SpecialPowers.wrap(window).docShell.editor;
+}
+
+function resetEditableContent(input) {
+  if (input instanceof HTMLInputElement ||
+      input instanceof HTMLTextAreaElement) {
+    input.value = "";
+    return;
+  }
+  input.innerHTML = "";
+}
+
+async function test_with_single_quote(input) {
+  let misspeltWords = [];
+
+  input.focus();
+  resetEditableContent(input);
+
+  synthesizeKey("d");
+  synthesizeKey("o");
+  synthesizeKey("e");
+  synthesizeKey("s");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(input, resolve); });
+  let editor = getEditor(input);
+  // isSpellingCheckOk is defined in spellcheck.js
+  ok(isSpellingCheckOk(editor, misspeltWords), "no misspelt words");
+
+  synthesizeKey("n");
+  synthesizeKey("\'");
+  is(input.value || input.textContent, "doesn\'", "");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(input, resolve); });
+  // XXX This won't work since mozInlineSpellWordUtil::SplitDOM removes
+  // last single quote unfortunately that is during inputting.
+  // isSpellingCheckOk is defined in spellcheck.js
+  todo_is(isSpellingCheckOk(editor, misspeltWords, true), true,
+          "don't run spellchecker during inputting word");
+
+  synthesizeKey(" ");
+  is(input.value || input.textContent, "doesn\' ", "");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(input, resolve); });
+  misspeltWords.push("doesn");
+  // isSpellingCheckOk is defined in spellcheck.js
+  ok(isSpellingCheckOk(editor, misspeltWords), "should run spellchecker");
+}
+
+async function test_with_twice_characters(input, ch) {
+  let misspeltWords = [];
+
+  input.focus();
+  resetEditableContent(input);
+
+  synthesizeKey("d");
+  synthesizeKey("o");
+  synthesizeKey("e");
+  synthesizeKey("s");
+  synthesizeKey("n");
+  synthesizeKey(ch);
+  synthesizeKey(ch);
+  is(input.value || input.textContent, "doesn" + ch + ch, "");
+
+  // trigger spellchecker
+  synthesizeKey(" ");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(input, resolve); });
+  misspeltWords.push("doesn");
+  let editor = getEditor(input);
+  // isSpellingCheckOk is defined in spellcheck.js
+  ok(isSpellingCheckOk(editor, misspeltWords), "should run spellchecker");
+}
+
+async function test_between_single_quote(input) {
+  let misspeltWords = [];
+
+  input.focus();
+  resetEditableContent(input);
+
+  synthesizeKey("\'");
+  synthesizeKey("t");
+  synthesizeKey("e");
+  synthesizeKey("s");
+  synthesizeKey("t");
+  synthesizeKey("\'");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(input, resolve); });
+  let editor = getEditor(input);
+  ok(isSpellingCheckOk(editor, misspeltWords),
+     "don't run spellchecker between single qoute");
+}
+
+async function test_with_email(input) {
+  let misspeltWords = [];
+
+  input.focus();
+  resetEditableContent(input);
+
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey("@");
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey(".");
+  synthesizeKey("c");
+  synthesizeKey("o");
+  synthesizeKey("m");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(input, resolve); });
+  let editor = getEditor(input);
+  ok(isSpellingCheckOk(editor, misspeltWords),
+     "don't run spellchecker for email address");
+
+  synthesizeKey(" ");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(input, resolve); });
+  ok(isSpellingCheckOk(editor, misspeltWords),
+     "no misspelt words due to email address");
+}
+
+async function test_with_url(input) {
+  let misspeltWords = [];
+
+  input.focus();
+  resetEditableContent(input);
+
+  synthesizeKey("h");
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey("p");
+  synthesizeKey(":");
+  synthesizeKey("/");
+  synthesizeKey("/");
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey("t");
+  synthesizeKey(".");
+  synthesizeKey("c");
+  synthesizeKey("o");
+  synthesizeKey("m");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(input, resolve); });
+  let editor = getEditor(input);
+  ok(isSpellingCheckOk(editor, misspeltWords),
+     "don't run spellchecker for URL");
+
+  synthesizeKey(" ");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(input, resolve); });
+  ok(isSpellingCheckOk(editor, misspeltWords),
+     "no misspelt words due to URL");
+}
+
+SimpleTest.waitForFocus(() => {
+  for (let n of ["input1", "textarea1", "edit1"])  {
+    add_task(test_with_single_quote.bind(null,
+                                         document.getElementById(n)));
+    add_task(test_with_twice_characters.bind(null,
+                                             document.getElementById(n),
+                                             "\'"));
+    add_task(test_with_twice_characters.bind(null,
+                                             document.getElementById(n),
+                                             String.fromCharCode(0x2019)));
+    add_task(test_between_single_quote.bind(null,
+                                            document.getElementById(n)));
+    add_task(test_with_email.bind(null, document.getElementById(n)));
+    add_task(test_with_url.bind(null, document.getElementById(n)));
+  }
+});
+</script>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1497480.html b/editor/spellchecker/tests/test_bug1497480.html
new file mode 100644
index 0000000000..a32e67370d
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1497480.html
@@ -0,0 +1,94 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1497480
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1497480</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <script src="spellcheck.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1497480">Mozilla Bug 1497480</a>
+<p id="display"></p>
+
+<div id="outOfTarget" contenteditable>Bug 1497480</div>
+<div id="light"></div>
+
+<script>
+
+/** Test for Bug 1497480 **/
+let gMisspeltWords = [];
+let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+const template = document.createElement("template");
+template.innerHTML = `<div id="target" contenteditable>Test</div>`;
+
+let shadow = document.getElementById("light").attachShadow({mode: "closed"});
+shadow.appendChild(template.content.cloneNode(true));
+
+let target = shadow.getElementById("target");
+let outOfTarget = document.getElementById("outOfTarget");
+
+function getEditor() {
+  var win = window;
+  var editingSession = SpecialPowers.wrap(win).docShell.editingSession;
+  return editingSession.getEditorForWindow(win);
+}
+
+// Wait for the page to be ready for testing
+add_task(async function() {
+  await new Promise((resolve) => {
+    SimpleTest.waitForFocus(() => {
+      SimpleTest.executeSoon(resolve);
+    }, window);
+  });
+
+  // Wait for first full spell-checking.
+  synthesizeMouseAtCenter(outOfTarget, {}, window);
+  await new Promise((resolve) => {
+    maybeOnSpellCheck(outOfTarget, function() {
+      resolve();
+    });
+  });
+});
+
+// Should perform spell-checking when anchor navigates away from ShadowDOM.
+add_task(async function() {
+  synthesizeMouseAtCenter(target, {}, window);
+  sendString(" spellechek");
+  gMisspeltWords.push("spellechek");
+  synthesizeMouseAtCenter(outOfTarget, {}, window);
+  await new Promise((resolve) => {
+    maybeOnSpellCheck(target, function() {
+      ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+         "Spell-checking should be performed when anchor navigates away from ShadowDOM");
+      SimpleTest.executeSoon(resolve);
+    });
+  });
+});
+
+// Should perform spell-checking when pressing enter in contenteditable in ShadowDOM.
+add_task(async function() {
+  synthesizeMouseAtCenter(target, {}, window);
+  sendString(" spellechck");
+  gMisspeltWords.push("spellechck");
+  synthesizeKey("KEY_Enter", {}, window);
+  await new Promise((resolve) => {
+    maybeOnSpellCheck(target, function() {
+      ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+         "Spell-checking should be performed when pressing enter in contenteditable in ShadowDOM");
+      SimpleTest.executeSoon(resolve);
+    });
+  });
+});
+
+</script>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1602526.html b/editor/spellchecker/tests/test_bug1602526.html
new file mode 100644
index 0000000000..62be07a53c
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1602526.html
@@ -0,0 +1,57 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Mozilla bug 1602526</title>
+  <link rel=stylesheet href="/tests/SimpleTest/test.css">
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/editor/spellchecker/tests/spellcheck.js"></script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1602526">Mozilla Bug 1602526</a>
+<p id="display"></p>
+<div id="content" style="display: none;">
+
+</div>
+
+<div id="contenteditable" contenteditable=true>kkkk&#xf6;kkkk</div>
+
+<script>
+const { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+SimpleTest.waitForExplicitFinish();
+
+function getEditor() {
+  return SpecialPowers.wrap(window).docShell.editor;
+}
+
+SimpleTest.waitForFocus(async () => {
+  let contenteditable = document.getElementById("contenteditable");
+  let misspeltWords = [];
+  misspeltWords.push("kkkk\u00f6kkkk");
+
+  contenteditable.focus();
+  window.getSelection().collapse(contenteditable.firstChild, contenteditable.firstChild.length);
+
+  synthesizeKey(" ");
+
+  // Run spell checker
+  await new Promise((resolve) => { maybeOnSpellCheck(contenteditable, resolve); });
+
+  synthesizeKey("a");
+  synthesizeKey("a");
+  synthesizeKey("a");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(contenteditable, resolve); });
+  let editor = getEditor();
+  // isSpellingCheckOk is defined in spellcheck.js
+  // eslint-disable-next-line no-undef
+  ok(isSpellingCheckOk(editor, misspeltWords), "correct word is seleced as misspell");
+
+  SimpleTest.finish();
+});
+</script>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1761273.html b/editor/spellchecker/tests/test_bug1761273.html
new file mode 100644
index 0000000000..65e3618194
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1761273.html
@@ -0,0 +1,96 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1761273
+-->
+<head>
+  <title>Test for Bug 1761273</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1761273">Mozilla Bug 1761273</a>
+<p id="display"></p>
+</div>
+
+<textarea id="editor" lang="en-US">heute ist ein guter Tag - today is a good day</textarea>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+const Ci = SpecialPowers.Ci;
+
+let {
+  getDictionaryContentPref,
+  onSpellCheck,
+} = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+/** Test for Bug 1402822 **/
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(start);
+async function start() {
+  let script = SpecialPowers.loadChromeScript(() => {
+    /* eslint-env mozilla/chrome-script */
+    // eslint-disable-next-line mozilla/use-services
+    let dir = Cc["@mozilla.org/file/directory_service;1"]
+                .getService(Ci.nsIProperties)
+                .get("CurWorkD", Ci.nsIFile);
+    dir.append("tests");
+    dir.append("editor");
+    dir.append("spellchecker");
+    dir.append("tests");
+
+    let hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                     .getService(Ci.mozISpellCheckingEngine);
+
+    // Install de-DE dictionary.
+    let de_DE = dir.clone();
+    de_DE.append("de-DE");
+    hunspell.addDirectory(de_DE);
+
+    addMessageListener("destroy", () => hunspell.removeDirectory(de_DE));
+    addMessageListener("de_DE-exists", () => de_DE.exists());
+  });
+  is(await script.sendQuery("de_DE-exists"), true,
+     "true expected (de_DE directory should exist)");
+
+  let textarea = document.getElementById("editor");
+  textarea.focus();
+
+  onSpellCheck(textarea, async () => {
+    let isc = SpecialPowers.wrap(textarea).editor.getInlineSpellChecker(true);
+    ok(isc, "Inline spell checker should exist after focus and spell check");
+    let spellchecker = isc.spellChecker;
+
+    // Setting the language to the language of the texteditor should not set the
+    // content preference.
+    await spellchecker.setCurrentDictionaries(["en-US"]);
+    let dictionaryContentPref = await getDictionaryContentPref();
+    is(dictionaryContentPref, "", "Content pref should be empty");
+
+    await spellchecker.setCurrentDictionaries(["en-US", "de-DE"]);
+    dictionaryContentPref = await getDictionaryContentPref();
+    is(dictionaryContentPref, "en-US,de-DE,", "Content pref should be en-US,de-DE,");
+
+    await spellchecker.setCurrentDictionaries(["de-DE"]);
+    dictionaryContentPref = await getDictionaryContentPref();
+    is(dictionaryContentPref, "de-DE,", "Content pref should be de-DE,");
+
+    // Remove the fake de_DE dictionary again.
+    await script.sendQuery("destroy");
+
+    // This will clear the content preferences and reset "spellchecker.dictionary".
+    await spellchecker.setCurrentDictionaries([]);
+    dictionaryContentPref = await getDictionaryContentPref();
+    is(dictionaryContentPref, "", "Content pref should be empty");
+
+    SimpleTest.finish();
+  });
+}
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1773802.html b/editor/spellchecker/tests/test_bug1773802.html
new file mode 100644
index 0000000000..7e9866817d
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1773802.html
@@ -0,0 +1,96 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1773802
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1773802</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1773802">Mozilla Bug 1773802</a>
+<p id="display"></p>
+</div>
+
+<textarea id="editor">correct правильный, incarrect непровильный</textarea>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+const Ci = SpecialPowers.Ci;
+
+let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+function getMisspelledWords(editor) {
+  return editor.selectionController.getSelection(Ci.nsISelectionController.SELECTION_SPELLCHECK).toString();
+}
+
+/** Test for Bug 1773802 **/
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(start);
+async function start() {
+  let script = SpecialPowers.loadChromeScript(() => {
+    /* eslint-env mozilla/chrome-script */
+    // eslint-disable-next-line mozilla/use-services
+    let dir = Cc["@mozilla.org/file/directory_service;1"]
+                .getService(Ci.nsIProperties)
+                .get("CurWorkD", Ci.nsIFile);
+    dir.append("tests");
+    dir.append("editor");
+    dir.append("spellchecker");
+    dir.append("tests");
+
+    let hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                     .getService(Ci.mozISpellCheckingEngine);
+
+    // Install ru-RU dictionary.
+    let ru_RU = dir.clone();
+    ru_RU.append("ru-RU");
+    hunspell.addDirectory(ru_RU);
+
+    addMessageListener("destroy", () => hunspell.removeDirectory(ru_RU));
+    addMessageListener("ru_RU-exists", () => ru_RU.exists());
+  });
+  is(await script.sendQuery("ru_RU-exists"), true,
+     "true expected (ru_RU directory should exist)");
+
+  let textarea = document.getElementById("editor");
+  let editor = SpecialPowers.wrap(textarea).editor;
+  textarea.focus();
+
+  maybeOnSpellCheck(textarea, () => {
+    let isc = SpecialPowers.wrap(textarea).editor.getInlineSpellChecker(false);
+    ok(isc, "Inline spell checker should exist after focus and spell check");
+    let spellchecker = isc.spellChecker;
+
+    spellchecker.setCurrentDictionaries(["en-US", "ru-RU"]).then(async () => {
+      textarea.blur();
+      textarea.focus();
+      maybeOnSpellCheck(textarea, async function() {
+        let currentDictionaries = spellchecker.getCurrentDictionaries();
+
+        is(currentDictionaries.length, 2, "expected two dictionaries");
+        is(currentDictionaries[0], "en-US", "expected en-US");
+        is(currentDictionaries[1], "ru-RU", "expected ru-RU");
+        is(getMisspelledWords(editor), "incarrectнепровильный", "some misspelled words expected: incarrect непровильный");
+
+        // Remove the fake ru_RU dictionary again.
+        await script.sendQuery("destroy");
+
+        // This will clear the content preferences and reset "spellchecker.dictionary".
+        spellchecker.setCurrentDictionaries([]).then(() => {
+          SimpleTest.finish();
+        });
+      });
+    });
+  });
+}
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug1837268.html b/editor/spellchecker/tests/test_bug1837268.html
new file mode 100644
index 0000000000..1467a328b5
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug1837268.html
@@ -0,0 +1,79 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Mozilla bug 1837268</title>
+  <link rel=stylesheet href="/tests/SimpleTest/test.css">
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/editor/spellchecker/tests/spellcheck.js"></script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1837268">Mozilla Bug 1837268</a>
+<p id="display"></p>
+<div id="content" style="display: none;">
+
+</div>
+
+<div id="contenteditable" contenteditable=true>aabbcc</div>
+
+<script>
+const { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+SimpleTest.waitForExplicitFinish();
+
+function getEditor() {
+  return SpecialPowers.wrap(window).docShell.editor;
+}
+
+SimpleTest.waitForFocus(async () => {
+  let contenteditable = document.getElementById("contenteditable");
+  contenteditable.addEventListener("beforeinput", (ev) => {
+    ev.preventDefault();
+    let text = contenteditable.textContent;
+    const sel = window.getSelection();
+    let offset = sel.anchorOffset;
+    switch (ev.inputType) {
+      case "insertText":
+        text = text.substring(0, offset) + ev.data + text.substring(offset);
+        offset += 1;
+        break;
+      case "deleteContentBackward":
+        text = text.substring(0, offset - 1) + text.substring(offset);
+        offset -= 1;
+        break;
+      default:
+        return;
+    }
+    if (contenteditable.firstChild) {
+      contenteditable.firstChild.nodeValue = text;
+    } else {
+      contenteditable.textContent = text;
+    }
+    sel.collapse(contenteditable.firstChild ?? contenteditable, offset);
+  });
+
+  let misspelledWords = [];
+  misspelledWords.push("aabbc"); // One c removed.
+
+  contenteditable.focus();
+  window.getSelection().collapse(contenteditable.firstChild, contenteditable.firstChild.length);
+
+  // Run spell checker
+  await new Promise((resolve) => { maybeOnSpellCheck(contenteditable, resolve); });
+
+  synthesizeKey("KEY_Backspace");
+  synthesizeKey(" ");
+
+  await new Promise((resolve) => { maybeOnSpellCheck(contenteditable, resolve); });
+  let editor = getEditor();
+  // isSpellingCheckOk is defined in spellcheck.js
+  // eslint-disable-next-line no-undef
+  ok(isSpellingCheckOk(editor, misspelledWords), "correct word is selected as misspelled");
+
+  SimpleTest.finish();
+});
+</script>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug338427.html b/editor/spellchecker/tests/test_bug338427.html
new file mode 100644
index 0000000000..20edb29012
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug338427.html
@@ -0,0 +1,61 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=338427
+-->
+<head>
+  <title>Test for Bug 338427</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=338427">Mozilla Bug 338427</a>
+<p id="display"></p>
+<div id="content">
+<textarea id="editor" lang="testing-XX" spellcheck="true"></textarea>
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+/** Test for Bug 338427 **/
+function init() {
+    var { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+      "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+    );
+    var textarea = document.getElementById("editor");
+    var editor = SpecialPowers.wrap(textarea).editor;
+    var spellchecker = editor.getInlineSpellChecker(true);
+    spellchecker.enableRealTimeSpell = true;
+    textarea.focus();
+
+    onSpellCheck(textarea, function() {
+        var list = spellchecker.spellChecker.GetDictionaryList();
+        ok(!!list.length, "At least one dictionary should be present");
+
+        var lang = list[0];
+        spellchecker.spellChecker.setCurrentDictionaries([lang]).then(() => {
+          onSpellCheck(textarea, function() {
+            try {
+                var dictionaries =
+                    spellchecker.spellChecker.getCurrentDictionaries();
+            } catch (e) {}
+            is(dictionaries.length, 1, "Expected one dictionary");
+            is(dictionaries[0], lang, "Unexpected spell check dictionary");
+
+            // This will clear the content preferences and reset "spellchecker.dictionary".
+            spellchecker.spellChecker.setCurrentDictionaries([]).then(() => {
+              SimpleTest.finish();
+            });
+          });
+        });
+    });
+}
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(init);
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug366682.html b/editor/spellchecker/tests/test_bug366682.html
new file mode 100644
index 0000000000..0191c599ab
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug366682.html
@@ -0,0 +1,65 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=366682
+-->
+<head>
+  <title>Test for Bug 366682</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <script src="spellcheck.js"></script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=366682">Mozilla Bug 366682</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 366682 **/
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(runTest);
+
+var gMisspeltWords;
+
+function getEdit() {
+  return document.getElementById("edit");
+}
+
+function editDoc() {
+  return getEdit().contentDocument;
+}
+
+function getEditor() {
+  var win = editDoc().defaultView;
+  var editingSession = SpecialPowers.wrap(win).docShell.editingSession;
+  return editingSession.getEditorForWindow(win);
+}
+
+function runTest() {
+  editDoc().body.innerHTML = "<div>errror and an other errror</div>";
+  gMisspeltWords = ["errror", "errror"];
+  editDoc().designMode = "on";
+  editDoc().defaultView.focus();
+
+  const { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  maybeOnSpellCheck(editDoc().documentElement, evalTest);
+}
+
+function evalTest() {
+  ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+     "All misspellings accounted for.");
+  SimpleTest.finish();
+}
+</script>
+</pre>
+
+<iframe id="edit" width="200" height="100" src="about:blank"></iframe>
+
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug432225.html b/editor/spellchecker/tests/test_bug432225.html
new file mode 100644
index 0000000000..19654eec06
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug432225.html
@@ -0,0 +1,72 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=432225
+-->
+<head>
+  <title>Test for Bug 432225</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <script src="spellcheck.js"></script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=432225">Mozilla Bug 432225</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 432225 **/
+
+let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(runTest);
+
+var gMisspeltWords = [];
+
+function getEdit() {
+  return document.getElementById("edit");
+}
+
+function editDoc() {
+  return getEdit().contentDocument;
+}
+
+function getEditor() {
+  var win = editDoc().defaultView;
+  var editingSession = SpecialPowers.wrap(win).docShell.editingSession;
+  return editingSession.getEditorForWindow(win);
+}
+
+function runTest() {
+  editDoc().designMode = "on";
+  setTimeout(function() { addWords(100); }, 0);
+}
+
+function addWords(aLimit) {
+  if (aLimit == 0) {
+    ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+       "All misspellings accounted for.");
+    SimpleTest.finish();
+    return;
+  }
+  getEdit().focus();
+  sendString("aa OK ");
+  gMisspeltWords.push("aa");
+  maybeOnSpellCheck(editDoc(), function() {
+    addWords(aLimit - 1);
+  });
+}
+</script>
+</pre>
+
+<iframe id="edit" width="200" height="100" src="about:blank"></iframe>
+
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug484181.html b/editor/spellchecker/tests/test_bug484181.html
new file mode 100644
index 0000000000..dab966bcde
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug484181.html
@@ -0,0 +1,73 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=484181
+-->
+<head>
+  <title>Test for Bug 484181</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <script src="spellcheck.js"></script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=484181">Mozilla Bug 484181</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 484181 **/
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(runTest);
+
+var gMisspeltWords;
+
+function getEditor() {
+  var win = window;
+  var editingSession = SpecialPowers.wrap(win).docShell.editingSession;
+  return editingSession.getEditorForWindow(win);
+}
+
+function append(str) {
+  var edit = document.getElementById("edit");
+  var editor = getEditor();
+  var sel = editor.selection;
+  sel.selectAllChildren(edit);
+  sel.collapseToEnd();
+  sendString(str);
+}
+
+function runTest() {
+  gMisspeltWords = ["haz", "cheezburger"];
+  var edit = document.getElementById("edit");
+  edit.focus();
+
+  const { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  maybeOnSpellCheck(edit, function() {
+    ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+       "All misspellings before editing are accounted for.");
+
+    append(" becaz I'm a lulcat!");
+    maybeOnSpellCheck(edit, function() {
+      gMisspeltWords.push("becaz");
+      gMisspeltWords.push("lulcat");
+      ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+         "All misspellings after typing are accounted for.");
+
+      SimpleTest.finish();
+    });
+  });
+}
+</script>
+</pre>
+
+<div><div></div><div id="edit" contenteditable="true">I can haz cheezburger</div></div>
+
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug596333.html b/editor/spellchecker/tests/test_bug596333.html
new file mode 100644
index 0000000000..bbd6aab7a0
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug596333.html
@@ -0,0 +1,135 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=596333
+-->
+<head>
+  <title>Test for Bug 596333</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <script src="spellcheck.js"></script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=596333">Mozilla Bug 596333</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 596333 **/
+const Ci = SpecialPowers.Ci;
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(runTest);
+
+var gMisspeltWords;
+var onSpellCheck;
+
+function getEditor() {
+  return SpecialPowers.wrap(document.getElementById("edit")).editor;
+}
+
+function append(str) {
+  var edit = document.getElementById("edit");
+  edit.focus();
+  edit.selectionStart = edit.selectionEnd = edit.value.length;
+  sendString(str);
+}
+
+function getLoadContext() {
+  return SpecialPowers.wrap(window).docShell.QueryInterface(Ci.nsILoadContext);
+}
+
+function paste(str) {
+  var Cc = SpecialPowers.Cc;
+  var trans = Cc["@mozilla.org/widget/transferable;1"].createInstance(Ci.nsITransferable);
+  trans.init(getLoadContext());
+  var s = Cc["@mozilla.org/supports-string;1"].createInstance(Ci.nsISupportsString);
+  s.data = str;
+  trans.setTransferData("text/plain", s);
+
+  let beforeInputEvent = null;
+  let inputEvent = null;
+  window.addEventListener("beforeinput", aEvent => { beforeInputEvent = aEvent; }, {once: true});
+  window.addEventListener("input", aEvent => { inputEvent = aEvent; }, {once: true});
+  getEditor().pasteTransferable(trans);
+  isnot(beforeInputEvent, null, '"beforeinput" event should be fired');
+  if (beforeInputEvent) {
+    is(beforeInputEvent.cancelable, true, '"beforeinput" event for "insertFromPaste" should be cancelable');
+    is(beforeInputEvent.inputType, "insertFromPaste", 'inputType of "beforeinput" event should be "insertFromPaste"');
+    is(beforeInputEvent.data, str, `data of "beforeinput" event should be "${str}"`);
+    is(beforeInputEvent.dataTransfer, null, 'dataTransfer of "beforeinput" event should be null on <textarea>');
+    is(beforeInputEvent.getTargetRanges().length, 0, 'getTargetRanges() of "beforeinput" event should return empty array on <textarea>');
+  }
+  is(inputEvent.type, "input", '"input" event should be fired');
+  is(inputEvent.inputType, "insertFromPaste", '"inputType of "input" event should be "insertFromPaste"');
+  is(inputEvent.data, str, `data of "input" event should be "${str}"`);
+  is(inputEvent.dataTransfer, null, 'dataTransfer of "input" event should be null on <textarea>');
+  is(inputEvent.getTargetRanges().length, 0, 'getTargetRanges() of "input" event should return empty array on <textarea>');
+}
+
+function runOnFocus() {
+  var edit = document.getElementById("edit");
+
+  gMisspeltWords = ["haz", "cheezburger"];
+  ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+     "All misspellings before editing are accounted for.");
+  append(" becaz I'm a lulcat!");
+  onSpellCheck(edit, function() {
+    gMisspeltWords.push("becaz");
+    gMisspeltWords.push("lulcat");
+    ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+       "All misspellings after typing are accounted for.");
+
+    // Now, type an invalid word, and instead of hitting "space" at the end, just blur
+    // the textarea and see if the spell check after the blur event catches it.
+    append(" workd");
+    edit.blur();
+    onSpellCheck(edit, function() {
+      gMisspeltWords.push("workd");
+      ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+         "All misspellings after blur are accounted for.");
+
+      // Also, test the case when we're entering the first word in a textarea
+      gMisspeltWords = ["workd"];
+      edit.value = "";
+      append("workd ");
+      onSpellCheck(edit, function() {
+        ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+           "Misspelling in the first entered word is accounted for.");
+
+        // Make sure that pasting would also trigger spell checking for the previous word
+        gMisspeltWords = ["workd"];
+        edit.value = "";
+        append("workd");
+        paste("           x");
+        onSpellCheck(edit, function() {
+          ok(isSpellingCheckOk(getEditor(), gMisspeltWords),
+             "Misspelling is accounted for after pasting.");
+
+          SimpleTest.finish();
+        });
+      });
+    });
+  });
+}
+
+function runTest() {
+  var edit = document.getElementById("edit");
+  edit.focus();
+
+  onSpellCheck = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  ).onSpellCheck;
+  onSpellCheck(edit, runOnFocus);
+}
+</script>
+</pre>
+
+<textarea id="edit">I can haz cheezburger</textarea>
+
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug636465.html b/editor/spellchecker/tests/test_bug636465.html
new file mode 100644
index 0000000000..aaa64c3a31
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug636465.html
@@ -0,0 +1,54 @@
+<!doctype html>
+<title>Mozilla bug 636465</title>
+<link rel=stylesheet href="/tests/SimpleTest/test.css">
+<script src="/tests/SimpleTest/EventUtils.js"></script>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<script src="/tests/SimpleTest/WindowSnapshot.js"></script>
+<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=636465"
+   target="_blank">Mozilla Bug 636465</a>
+<input id="x" value="foobarbaz" spellcheck="true" style="background-color: transparent; border: transparent;">
+<script>
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+  const { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  var x = document.getElementById("x");
+  x.focus();
+  onSpellCheck(x, function() {
+    x.blur();
+    var spellCheckTrue = snapshotWindow(window);
+    x.setAttribute("spellcheck", "false");
+    var spellCheckFalse = snapshotWindow(window);
+    x.setAttribute("spellcheck", "true");
+    x.focus();
+    onSpellCheck(x, function() {
+      x.blur();
+      var spellCheckTrueAgain = snapshotWindow(window);
+      x.removeAttribute("spellcheck");
+      var spellCheckNone = snapshotWindow(window);
+      var ret = compareSnapshots(spellCheckTrue, spellCheckFalse, false)[0];
+      ok(ret,
+         "Setting the spellcheck attribute to false should work");
+      if (!ret) {
+        ok(false, "\nspellCheckTrue: " + spellCheckTrue.toDataURL() + "\nspellCheckFalse: " + spellCheckFalse.toDataURL());
+      }
+      ret = compareSnapshots(spellCheckTrue, spellCheckTrueAgain, true)[0];
+      ok(ret,
+         "Setting the spellcheck attribute back to true should work");
+      if (!ret) {
+        ok(false, "\nspellCheckTrue: " + spellCheckTrue.toDataURL() + "\nspellCheckTrueAgain: " + spellCheckTrueAgain.toDataURL());
+      }
+      ret = compareSnapshots(spellCheckNone, spellCheckFalse, true)[0];
+      ok(ret,
+         "Unsetting the spellcheck attribute should work");
+      if (!ret) {
+        ok(false, "\spellCheckNone: " + spellCheckNone.toDataURL() + "\nspellCheckFalse: " + spellCheckFalse.toDataURL());
+      }
+      SimpleTest.finish();
+    });
+  });
+}
+addLoadEvent(runTest);
+</script>
diff --git a/editor/spellchecker/tests/test_bug678842.html b/editor/spellchecker/tests/test_bug678842.html
new file mode 100644
index 0000000000..b328e5a8ff
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug678842.html
@@ -0,0 +1,106 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=678842
+-->
+<head>
+  <title>Test for Bug 678842</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=678842">Mozilla Bug 678842</a>
+<p id="display"></p>
+<iframe id="content"></iframe>
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+/** Test for Bug 678842 **/
+SimpleTest.waitForExplicitFinish();
+var content = document.getElementById("content");
+// load a subframe containing an editor with a defined unknown lang. At first
+// load, it will set dictionary to en-US. At second load, it will return current
+// dictionary. So, we can check, dictionary is correctly remembered between
+// loads.
+
+var firstLoad = true;
+var script;
+
+var loadListener = async function(evt) {
+  if (firstLoad) {
+    script = SpecialPowers.loadChromeScript(function() {
+      /* eslint-env mozilla/chrome-script */
+      // eslint-disable-next-line mozilla/use-services
+      var dir = Cc["@mozilla.org/file/directory_service;1"]
+                  .getService(Ci.nsIProperties)
+                  .get("CurWorkD", Ci.nsIFile);
+      dir.append("tests");
+      dir.append("editor");
+      dir.append("spellchecker");
+      dir.append("tests");
+
+      var hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                       .getService(Ci.mozISpellCheckingEngine);
+
+      // Install en-GB dictionary.
+      let en_GB = dir.clone();
+      en_GB.append("en-GB");
+      hunspell.addDirectory(en_GB);
+
+      addMessageListener("en_GB-exists", () => en_GB.exists());
+      addMessageListener("destroy", () => hunspell.removeDirectory(en_GB));
+    });
+    is(await script.sendQuery("en_GB-exists"), true,
+       "true expected (en-GB directory should exist)");
+  }
+
+  var doc = evt.target.contentDocument;
+  var elem = doc.getElementById("textarea");
+  var editor = SpecialPowers.wrap(elem).editor;
+  editor.setSpellcheckUserOverride(true);
+  var inlineSpellChecker = editor.getInlineSpellChecker(true);
+
+  const { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  onSpellCheck(elem, async function() {
+    let spellchecker = inlineSpellChecker.spellChecker;
+    let currentDictionaries = spellchecker.getCurrentDictionaries();
+    is(currentDictionaries.length, 1, "expected one dictionary");
+    let currentDictionary = currentDictionaries[0];
+
+    if (firstLoad) {
+      firstLoad = false;
+
+       // First time around, the dictionary defaults to the locale.
+      is(currentDictionary, "en-US", "unexpected lang " + currentDictionary + " instead of en-US");
+
+      // Select en-GB.
+      spellchecker.setCurrentDictionaries(["en-GB"]).then(() => {
+        content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/bug678842_subframe.html?firstload=false";
+      });
+    } else {
+      is(currentDictionary, "en-GB", "unexpected lang " + currentDictionary + " instead of en-GB");
+      content.removeEventListener("load", loadListener);
+
+      // Remove the fake en-GB dictionary again, since it's otherwise picked up by later tests.
+      await script.sendQuery("destroy");
+
+      // This will clear the content preferences and reset "spellchecker.dictionary".
+      spellchecker.setCurrentDictionaries([]).then( () => {
+        SimpleTest.finish();
+      });
+    }
+  });
+};
+
+content.addEventListener("load", loadListener);
+
+content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/bug678842_subframe.html?firstload=true";
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug697981.html b/editor/spellchecker/tests/test_bug697981.html
new file mode 100644
index 0000000000..8ef5dbcd92
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug697981.html
@@ -0,0 +1,137 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=697981
+-->
+<head>
+  <title>Test for Bug 697981</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=697981">Mozilla Bug 697981</a>
+<p id="display"></p>
+</div>
+
+<textarea id="de-DE" lang="de-DE" onfocus="deFocus()">German heute ist ein guter Tag</textarea>
+<textarea id="en-US" lang="en-US" onfocus="enFocus()">Nogoodword today is a nice day</textarea>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+function getMisspelledWords(editor) {
+  return editor.selectionController.getSelection(SpecialPowers.Ci.nsISelectionController.SELECTION_SPELLCHECK).toString();
+}
+
+var elem_de;
+var editor_de;
+var script;
+
+var { maybeOnSpellCheck, onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+/** Test for Bug 697981 **/
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(async function() {
+  script = SpecialPowers.loadChromeScript(function() {
+    /* eslint-env mozilla/chrome-script */
+    // eslint-disable-next-line mozilla/use-services
+    var dir = Cc["@mozilla.org/file/directory_service;1"]
+                .getService(Ci.nsIProperties)
+                .get("CurWorkD", Ci.nsIFile);
+    dir.append("tests");
+    dir.append("editor");
+    dir.append("spellchecker");
+    dir.append("tests");
+
+    var hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                     .getService(Ci.mozISpellCheckingEngine);
+
+    // Install de-DE dictionary.
+    var de_DE = dir.clone();
+    de_DE.append("de-DE");
+    hunspell.addDirectory(de_DE);
+
+    addMessageListener("de_DE-exists", () => de_DE.exists());
+    addMessageListener("destroy", () => hunspell.removeDirectory(de_DE));
+  });
+  is(await script.sendQuery("de_DE-exists"), true,
+     "true expected (de_DE directory should exist)");
+
+  document.getElementById("de-DE").focus();
+});
+
+function deFocus() {
+  elem_de = document.getElementById("de-DE");
+  editor_de = SpecialPowers.wrap(elem_de).editor;
+  editor_de.setSpellcheckUserOverride(true);
+  var inlineSpellChecker = editor_de.getInlineSpellChecker(true);
+
+  maybeOnSpellCheck(elem_de, function() {
+    var spellchecker = inlineSpellChecker.spellChecker;
+    try {
+      var currentDictionaries = spellchecker.getCurrentDictionaries();
+    } catch (e) {}
+
+    // Check that the German dictionary is loaded and that the spell check has worked.
+    is(currentDictionaries.length, 1, "expected one dictionary");
+    is(currentDictionaries[0], "de-DE", "expected de-DE");
+    is(getMisspelledWords(editor_de), "German", "one misspelled word expected: German");
+
+    // Now focus the other textarea, which requires English spelling.
+    document.getElementById("en-US").focus();
+  });
+}
+
+function enFocus() {
+  var elem_en = document.getElementById("en-US");
+  var editor_en = SpecialPowers.wrap(elem_en).editor;
+  editor_en.setSpellcheckUserOverride(true);
+  var inlineSpellChecker = editor_en.getInlineSpellChecker(true);
+
+  onSpellCheck(elem_en, async function() {
+    let spellchecker = inlineSpellChecker.spellChecker;
+    let currentDictionaries = spellchecker.getCurrentDictionaries();
+
+    // Check that the English dictionary is loaded and that the spell check has worked.
+    is(currentDictionaries.length, 1, "expected one dictionary");
+    is(currentDictionaries[0], "en-US", "expected en-US");
+    is(getMisspelledWords(editor_en), "Nogoodword", "one misspelled word expected: Nogoodword");
+
+    // So far all was boring. The important thing is whether the spell check result
+    // in the de-DE editor is still the same. After losing focus, no spell check
+    // updates should take place there.
+    is(getMisspelledWords(editor_de), "German", "one misspelled word expected: German");
+
+    // Remove the fake de_DE dictionary again.
+    await script.sendQuery("destroy");
+
+    // Focus again, so the spelling gets updated, but before we need to kill the focus handler.
+    elem_de.onfocus = null;
+    elem_de.blur();
+    elem_de.focus();
+
+    // After removal, the de_DE editor should refresh the spelling with en-US.
+    maybeOnSpellCheck(elem_de, function() {
+      spellchecker = inlineSpellChecker.spellChecker;
+      try {
+        currentDictionaries = spellchecker.getCurrentDictionaries();
+      } catch (e) {}
+
+      // Check that the default English dictionary is loaded and that the spell check has worked.
+      is(currentDictionaries.length, 1, "expected one dictionary");
+      is(currentDictionaries[0], "en-US", "expected en-US");
+      // eslint-disable-next-line no-useless-concat
+      is(getMisspelledWords(editor_de), "heute" + "ist" + "ein" + "guter",
+         "some misspelled words expected: heute ist ein guter");
+
+      SimpleTest.finish();
+    });
+  });
+}
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_bug717433.html b/editor/spellchecker/tests/test_bug717433.html
new file mode 100644
index 0000000000..322e0d47d8
--- /dev/null
+++ b/editor/spellchecker/tests/test_bug717433.html
@@ -0,0 +1,111 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=717433
+-->
+<head>
+  <title>Test for Bug 717433</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=717433">Mozilla Bug 717433</a>
+<p id="display"></p>
+<iframe id="content"></iframe>
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+/** Test for Bug 717433 **/
+SimpleTest.waitForExplicitFinish();
+var content = document.getElementById("content");
+// Load a subframe containing an editor with language "en". At first
+// load, it will set the dictionary to en-GB or en-US. We set the other one.
+// At second load, it will return the current dictionary. We can check that the
+// dictionary is correctly remembered between loads.
+
+var firstLoad = true;
+var expected = "";
+var script;
+
+var loadListener = async function(evt) {
+  if (firstLoad) {
+    script = SpecialPowers.loadChromeScript(function() {
+      /* eslint-env mozilla/chrome-script */
+      // eslint-disable-next-line mozilla/use-services
+      var dir = Cc["@mozilla.org/file/directory_service;1"]
+                  .getService(Ci.nsIProperties)
+                  .get("CurWorkD", Ci.nsIFile);
+      dir.append("tests");
+      dir.append("editor");
+      dir.append("spellchecker");
+      dir.append("tests");
+
+      var hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                       .getService(Ci.mozISpellCheckingEngine);
+
+      // Install en-GB dictionary.
+      var en_GB = dir.clone();
+      en_GB.append("en-GB");
+      hunspell.addDirectory(en_GB);
+
+      addMessageListener("en_GB-exists", () => en_GB.exists());
+      addMessageListener("destroy", () => hunspell.removeDirectory(en_GB));
+    });
+    is(await script.sendQuery("en_GB-exists"), true,
+       "true expected (en-GB directory should exist)");
+  }
+
+  var doc = evt.target.contentDocument;
+  var elem = doc.getElementById("textarea");
+  var editor = SpecialPowers.wrap(elem).editor;
+  editor.setSpellcheckUserOverride(true);
+  var inlineSpellChecker = editor.getInlineSpellChecker(true);
+
+  const { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  onSpellCheck(elem, async function() {
+    let spellchecker = inlineSpellChecker.spellChecker;
+    let currentDictionaries = spellchecker.getCurrentDictionaries();
+
+    is(currentDictionaries.length, 1, "expected one dictionary");
+    let currentDictionary = currentDictionaries[0];
+
+    if (firstLoad) {
+      firstLoad = false;
+
+      // First time around, we get a random dictionary based on the language "en".
+      if (currentDictionary == "en-GB") {
+        expected = "en-US";
+      } else if (currentDictionary == "en-US") {
+        expected = "en-GB";
+      } else {
+        is(true, false, "Neither en-US nor en-GB are current");
+      }
+      spellchecker.setCurrentDictionaries([expected]).then(() => {
+        content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/bug717433_subframe.html?firstload=false";});
+    } else {
+      is(currentDictionary, expected, expected + " expected");
+      content.removeEventListener("load", loadListener);
+
+      // Remove the fake en-GB dictionary again, since it's otherwise picked up by later tests.
+      await script.sendQuery("destroy");
+
+      // This will clear the content preferences and reset "spellchecker.dictionary".
+      spellchecker.setCurrentDictionaries([]).then(() => {
+        SimpleTest.finish();
+      });
+    }
+  });
+};
+
+content.addEventListener("load", loadListener);
+
+content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/bug717433_subframe.html?firstload=true";
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_multiple_content_languages.html b/editor/spellchecker/tests/test_multiple_content_languages.html
new file mode 100644
index 0000000000..49d3bb5ace
--- /dev/null
+++ b/editor/spellchecker/tests/test_multiple_content_languages.html
@@ -0,0 +1,176 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Test for multiple Content-Language values</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<p id="display"></p>
+<iframe id="content"></iframe>
+
+<pre id="test">
+<script class="testbody">
+
+/** Test for multiple Content-Language values **/
+/** Visit the elements defined above and check the dictionaries we got **/
+SimpleTest.waitForExplicitFinish();
+var content = document.getElementById("content");
+
+var tests = [
+    // text area, value of spellchecker.dictionary, result.
+    // Result: Document language.
+    [ "none",  "", ["en-US", "en-GB"] ],
+
+    // Result: Element language.
+    [ "en-GB", "", ["en-GB"] ],
+    // Result: Random en-* or en-US (if application locale is en-US).
+    [ "en-ZA-not-avail", "", ["*"] ],
+    [ "en",              "", ["*"] ],
+    // Result: Locale.
+    [ "ko-not-avail",    "", ["en-US"] ],
+
+    // Result: Document language, plus preference value in all cases.
+    [ "none",            "en-AU", ["en-US", "en-GB", "en-AU"] ],
+    [ "en-ZA-not-avail", "en-AU", ["en-AU"] ],
+    [ "ko-not-avail",    "en-AU", ["en-AU"] ],
+
+    // Result: Document language, plus first matching preference language.
+    [ "none",            "en-AU,en-US", ["en-US", "en-GB", "en-AU"] ],
+    // Result: First matching preference language.
+    [ "en-ZA-not-avail", "en-AU,en-US", ["en-AU"] ],
+    // Result: Fall back to preference languages.
+    [ "ko-not-avail",    "en-AU,en-US", ["en-AU", "en-US"] ],
+
+    // Result: Random en-*.
+    [ "en-ZA-not-avail", "de-DE", ["*"] ],
+    // Result: Preference value.
+    [ "ko-not-avail",    "de-DE", ["de-DE"] ],
+  ];
+
+var loadCount = 0;
+var retrying = false;
+var script;
+
+var loadListener = async function(evt) {
+  if (loadCount == 0) {
+    script = SpecialPowers.loadChromeScript(function() {
+      /* eslint-env mozilla/chrome-script */
+      // eslint-disable-next-line mozilla/use-services
+      var dir = Cc["@mozilla.org/file/directory_service;1"]
+                  .getService(Ci.nsIProperties)
+                  .get("CurWorkD", Ci.nsIFile);
+      dir.append("tests");
+      dir.append("editor");
+      dir.append("spellchecker");
+      dir.append("tests");
+
+      var hunspell = Cc["@mozilla.org/spellchecker/engine;1"]
+                       .getService(Ci.mozISpellCheckingEngine);
+
+      // Install en-GB, en-AU and de-DE dictionaries.
+      var en_GB = dir.clone();
+      var en_AU = dir.clone();
+      var de_DE = dir.clone();
+      en_GB.append("en-GB");
+      en_AU.append("en-AU");
+      de_DE.append("de-DE");
+      hunspell.addDirectory(en_GB);
+      hunspell.addDirectory(en_AU);
+      hunspell.addDirectory(de_DE);
+
+      addMessageListener("check-existence",
+                         () => [en_GB.exists(), en_AU.exists(),
+                                de_DE.exists()]);
+      addMessageListener("destroy", () => {
+        hunspell.removeDirectory(en_GB);
+        hunspell.removeDirectory(en_AU);
+        hunspell.removeDirectory(de_DE);
+      });
+    });
+    var existenceChecks = await script.sendQuery("check-existence");
+    is(existenceChecks[0], true, "true expected (en-GB directory should exist)");
+    is(existenceChecks[1], true, "true expected (en-AU directory should exist)");
+    is(existenceChecks[2], true, "true expected (de-DE directory should exist)");
+  }
+
+  SpecialPowers.pushPrefEnv({set: [["spellchecker.dictionary", tests[loadCount][1]]]},
+                            function() { continueTest(evt); });
+};
+
+function continueTest(evt) {
+  var doc = evt.target.contentDocument;
+  var elem = doc.getElementById(tests[loadCount][0]);
+  var editor = SpecialPowers.wrap(elem).editor;
+  editor.setSpellcheckUserOverride(true);
+  var inlineSpellChecker = editor.getInlineSpellChecker(true);
+  const is_en_US = SpecialPowers.Services.locale.appLocaleAsBCP47 == "en-US";
+
+  const { onSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  onSpellCheck(elem, async function() {
+    var spellchecker = inlineSpellChecker.spellChecker;
+    let currentDictionaries;
+    try {
+      currentDictionaries = spellchecker.getCurrentDictionaries();
+    } catch (e) {}
+
+    if (!currentDictionaries && !retrying) {
+      // It's possible for an asynchronous font-list update to cause a reflow
+      // that disrupts the async spell-check and results in not getting a
+      // current dictionary here; if that happens, we retry the same testcase
+      // by reloading the iframe without bumping loadCount.
+      info(`No current dictionary: retrying testcase ${loadCount}`);
+      retrying = true;
+    } else {
+      let expectedDictionaries = tests[loadCount][2];
+      let dictionaryArray = Array.from(currentDictionaries);
+      is(
+        dictionaryArray.length,
+        expectedDictionaries.length,
+        "Expected matching dictionary count"
+      );
+      if (expectedDictionaries[0] != "*") {
+        ok(
+          dictionaryArray.every(dict => expectedDictionaries.includes(dict)),
+          "active dictionaries should match expectation"
+        );
+      } else if (is_en_US && tests[loadCount][0].startsWith("en")) {
+        // Current application locale is en-US and content lang is en or
+        // en-unknown, so we should use en-US dictionary as default.
+        is(
+          dictionaryArray[0],
+          "en-US",
+          "expected en-US that is application locale"
+        );
+      } else {
+        let dict = dictionaryArray[0];
+        var gotEn = (dict == "en-GB" || dict == "en-AU" || dict == "en-US");
+        is(gotEn, true, "expected en-AU or en-GB or en-US");
+      }
+
+      loadCount++;
+      retrying = false;
+    }
+
+    if (loadCount < tests.length) {
+      // Load the iframe again.
+      content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/multiple_content_languages_subframe.html?firstload=false";
+    } else {
+      // Remove the fake  dictionaries again, since it's otherwise picked up by later tests.
+      await script.sendQuery("destroy");
+
+      SimpleTest.finish();
+    }
+  });
+}
+
+content.addEventListener("load", loadListener);
+
+content.src = "http://mochi.test:8888/tests/editor/spellchecker/tests/multiple_content_languages_subframe.html?firstload=true";
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_nsIEditorSpellCheck_ReplaceWord.html b/editor/spellchecker/tests/test_nsIEditorSpellCheck_ReplaceWord.html
new file mode 100644
index 0000000000..a92c9f2f19
--- /dev/null
+++ b/editor/spellchecker/tests/test_nsIEditorSpellCheck_ReplaceWord.html
@@ -0,0 +1,64 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Test for nsIEditorSpellCheck.ReplaceWord()</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
+</head>
+<body>
+<div contenteditable spellcheck="true" lang="en-US"></div>
+<script>
+"use strict";
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(async () => {
+  const { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+  const editor = document.querySelector("div[contenteditable]");
+  async function replaceWord(aMisspelledWord, aCorrectWord, aReplaceAll) {
+    const editorObj = SpecialPowers.wrap(window).docShell.editingSession.getEditorForWindow(window);
+    const inlineSpellChecker = editorObj.getInlineSpellChecker(true);
+    await new Promise(resolve => maybeOnSpellCheck(editor, resolve));
+    const editorSpellCheck = inlineSpellChecker.spellChecker;
+    editorObj.beginTransaction();
+    try {
+      editorSpellCheck.ReplaceWord(aMisspelledWord, aCorrectWord, aReplaceAll);
+    } catch (e) {
+      ok(false, `Unexpected exception: ${e.message}`);
+    }
+    editorObj.endTransaction();
+    editorSpellCheck.GetNextMisspelledWord();
+  }
+
+  async function testReplaceAllMisspelledWords(aCorrectWord) {
+    editor.innerHTML = "<p>def abc def<br>abc def abc</p><p>abc def abc<br>def abc def</p>";
+    editor.focus();
+    editor.getBoundingClientRect();
+    await replaceWord("abc", aCorrectWord, true);
+    is(
+      editor.innerHTML,
+      `<p>def ${aCorrectWord} def<br>${aCorrectWord} def ${aCorrectWord}</p><p>${aCorrectWord} def ${aCorrectWord}<br>def ${aCorrectWord} def</p>`,
+      `nsIEditorSpellCheck.ReplaceWord(..., true) should replace all misspelled words with ${
+        (() => {
+          if (aCorrectWord.length > "abc".length) {
+            return "longer";
+          }
+          return aCorrectWord.length < "abc".length ? "shorter" : "same length"
+        })()
+      } correct word`
+    );
+    editor.blur();
+    editor.getBoundingClientRect();
+  }
+  await testReplaceAllMisspelledWords("ABC");
+  await testReplaceAllMisspelledWords("ABC!");
+  await testReplaceAllMisspelledWords("AB");
+
+  // TODO: Add tests for not all replacing cases.
+
+  SimpleTest.finish();
+});
+</script>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_spellcheck_after_edit.html b/editor/spellchecker/tests/test_spellcheck_after_edit.html
new file mode 100644
index 0000000000..24806addee
--- /dev/null
+++ b/editor/spellchecker/tests/test_spellcheck_after_edit.html
@@ -0,0 +1,194 @@
+<!doctype html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Spellcheck result after edit</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<script>
+let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+function waitForTick() {
+  return new Promise(resolve =>
+    SimpleTest.executeSoon(
+      () => requestAnimationFrame(
+        () => requestAnimationFrame(resolve)
+      )
+    )
+  );
+}
+
+async function waitForOnSpellCheck(
+  aSpellCheckSelection,
+  aEditingHost,
+  aWaitForNumberOfMisspelledWords,
+  aWhen
+) {
+  info(`Waiting for onSpellCheck (${aWhen})...`);
+  for (let retry = 0; retry < 100; retry++) {
+    await waitForTick();
+    await new Promise(resolve => maybeOnSpellCheck(aEditingHost, resolve));
+    if (aWaitForNumberOfMisspelledWords === 0) {
+      if (aSpellCheckSelection.rangeCount === 0) {
+        break;
+      }
+    } else if (aSpellCheckSelection.rangeCount >= aWaitForNumberOfMisspelledWords) {
+      break;
+    }
+  }
+}
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(async () => {
+  /**
+   * test object should have:
+   *   init function
+   *     @param normalSel       The normal selection for the editing host
+   *     @param editingHost     The editing host of the editor
+   *     @return                Number of misspelled word in the editor
+   *
+   *  run function
+   *     @param editingHost     The editing host of the editor
+   *     @return                Expected number of misspelled word in the editor
+   *
+   *  check function
+   *     @param spellCheckSel   The spellcheck selection for the editing host
+   *     @param editingHost     The editing host of the editor
+   */
+  for (const test of [
+      {
+        init: (normalSel, editingHost) => {
+          info("Staring to test spellcheck of misspelled word after joining paragraphs");
+          editingHost.innerHTML = "<p>It is</p><p>what I want</p>";
+          normalSel.collapse(editingHost.querySelector("p + p").firstChild, 0);
+          return 0;
+        },
+        run: (editingHost) => {
+          document.execCommand("delete");
+          return 0;
+        },
+        check: (spellCheckSel, editingHost) => {
+          is(
+            spellCheckSel.rangeCount,
+            0,
+            "The joined misspelled word shouldn't be marked as misspelled word because caret is in the word"
+          );
+        },
+      },
+      {
+        init: (normalSel, editingHost) => {
+          info("Staring to test spellcheck of correct word after joining paragraphs");
+          editingHost.innerHTML = "<p>It's beco</p><p>ming nicer</p>";
+          normalSel.collapse(editingHost.querySelector("p + p").firstChild, 0);
+          return 2;
+        },
+        run: (editingHost) => {
+          document.execCommand("delete");
+          return 0;
+        },
+        check: (spellCheckSel, editingHost) => {
+          is(
+            spellCheckSel.rangeCount,
+            0,
+            "There shouldn't be misspelled word after joining separated word anyway"
+          );
+        },
+      },
+      {
+        init: (normalSel, editingHost) => {
+          info("Staring to test spellcheck of correct words after splitting a paragraph");
+          editingHost.innerHTML = "<p>It iswhat I want</p>";
+          normalSel.collapse(editingHost.querySelector("p").firstChild, "It is".length);
+          return 1;
+        },
+        run: (editingHost) => {
+          document.execCommand("insertParagraph");
+          return 0;
+        },
+        check: (spellCheckSel, editingHost) => {
+          is(
+            spellCheckSel.rangeCount,
+            0,
+            "No word should be marked as misspelled after split"
+          );
+        },
+      },
+      {
+        init: (normalSel, editingHost) => {
+          info("Staring to test spellcheck of misspelled words after splitting a paragraph");
+          editingHost.innerHTML = "<p>It's becoming nicer</p>";
+          normalSel.collapse(editingHost.querySelector("p").firstChild, "It's beco".length);
+          return 0;
+        },
+        run: (editingHost) => {
+          document.execCommand("insertParagraph");
+          return 1;
+        },
+        check: (spellCheckSel, editingHost) => {
+          is(
+            spellCheckSel.rangeCount,
+            1,
+            "The split word in the first paragraph should be marked as misspelled, but the second paragraph's should be so because of caret is in it"
+          );
+          if (!spellCheckSel.rangeCount) {
+            return;
+          }
+          is(
+            SpecialPowers.unwrap(spellCheckSel.getRangeAt(0).startContainer),
+            editingHost.querySelector("p").firstChild,
+            "First misspelled word should start in the first child of the first <p>"
+          );
+          is(
+            SpecialPowers.unwrap(spellCheckSel.getRangeAt(0).endContainer),
+            editingHost.querySelector("p").firstChild,
+            "First misspelled word should end in the first child of the first <p>"
+          );
+          is(
+            spellCheckSel.getRangeAt(0).startOffset,
+            "It's ".length,
+            "First misspelled word should start after 'It '"
+          );
+          is(
+            spellCheckSel.getRangeAt(0).endOffset,
+            "It's beco".length,
+            "First misspelled word should end by after 'bec'"
+          );
+        },
+      },
+    ]) {
+    const editingHost = document.createElement("div");
+    editingHost.setAttribute("contenteditable", "");
+    editingHost.setAttribute("spellcheck", "true");
+    document.body.appendChild(editingHost);
+    editingHost.focus();
+    const editor =
+      SpecialPowers.wrap(window).docShell.editingSession.getEditorForWindow(window);
+    const nsISelectionController = SpecialPowers.Ci.nsISelectionController;
+    const normalSel = editor.selectionController.getSelection(
+        nsISelectionController.SELECTION_NORMAL
+    );
+    const spellCheckSel = editor.selectionController.getSelection(
+      nsISelectionController.SELECTION_SPELLCHECK
+    );
+    const initialMisspelledWords = test.init(normalSel, editingHost);
+    await waitForOnSpellCheck(
+      spellCheckSel, editingHost, initialMisspelledWords, "before edit"
+    );
+    await waitForTick();
+    const expectedMisspelledWords = test.run(editingHost);
+    await waitForOnSpellCheck(
+      spellCheckSel, editingHost, expectedMisspelledWords, "after edit"
+    );
+    test.check(spellCheckSel, editingHost);
+    editingHost.remove();
+    await waitForTick();
+  }
+  SimpleTest.finish();
+});
+</script>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_spellcheck_after_pressing_navigation_key.html b/editor/spellchecker/tests/test_spellcheck_after_pressing_navigation_key.html
new file mode 100644
index 0000000000..b1f36161ac
--- /dev/null
+++ b/editor/spellchecker/tests/test_spellcheck_after_pressing_navigation_key.html
@@ -0,0 +1,77 @@
+<!doctype html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1729653
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1729653</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<textarea rows="20" cols="50">That undfgdfg seems OK.</textarea>
+<script>
+let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+);
+
+function waitForTick() {
+  return new Promise(resolve => SimpleTest.executeSoon(resolve));
+}
+
+function waitForOnSpellCheck(aTextArea) {
+  info("Waiting for onSpellCheck...");
+  return new Promise(resolve => maybeOnSpellCheck(aTextArea, resolve));
+}
+
+/** Test for Bug 1729653 **/
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(async () => {
+  const textarea = document.querySelector("textarea");
+  textarea.focus();
+  textarea.selectionStart = textarea.selectionEnd = "That undfgdfg".length;
+  const editor = SpecialPowers.wrap(textarea).editor;
+  const nsISelectionController = SpecialPowers.Ci.nsISelectionController;
+  const selection = editor.selectionController.getSelection(nsISelectionController.SELECTION_SPELLCHECK);
+  const spellChecker = SpecialPowers.Cu.createSpellChecker();
+  spellChecker.InitSpellChecker(editor, false);
+  info("Waiting for current dictionary update...");
+  await new Promise(resolve => spellChecker.UpdateCurrentDictionary(resolve));
+  if (selection.rangeCount === 0) {
+    await waitForOnSpellCheck(textarea);
+  }
+  if (selection.rangeCount == 1) {
+    is(
+      selection.getRangeAt(0).toString(),
+      "undfgdfg",
+      "\"undfgdfg\" should be marked as misspelled word at start"
+    );
+  } else {
+    is(selection.rangeCount, 1, "We should have a misspelled word at start");
+  }
+  synthesizeKey(" ");
+  synthesizeKey("KEY_Backspace");
+  textarea.addEventListener("keydown", event => {
+    event.stopImmediatePropagation();  // This shouldn't block spellchecker to handle it.
+  }, {once: true});
+  synthesizeKey("KEY_End");
+  await waitForTick();
+  if (selection.rangeCount === 0) {
+    await waitForOnSpellCheck(textarea);
+  }
+  if (selection.rangeCount == 1) {
+    is(
+      selection.getRangeAt(0).toString(),
+      "undfgdfg",
+      "\"undfgdfg\" should be marked as misspelled word at end"
+    );
+  } else {
+    is(selection.rangeCount, 1, "We should have a misspelled word at end");
+  }
+  SimpleTest.finish();
+});
+</script>
+</body>
+</html>
diff --git a/editor/spellchecker/tests/test_spellcheck_selection.html b/editor/spellchecker/tests/test_spellcheck_selection.html
new file mode 100644
index 0000000000..983f67c51f
--- /dev/null
+++ b/editor/spellchecker/tests/test_spellcheck_selection.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Bug 1779846: Test enableSelectionChecking=true on nsIEditorSpellCheck.InitSpellChecker</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" href="/tests/SimpleTest/test.css" />
+
+<div contenteditable lang="en-US">missspelled</div>
+
+<script>
+add_task(async function() {
+  await new Promise(resolve => SimpleTest.waitForFocus(resolve));
+
+  let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+
+  let editingHost = document.querySelector("div[contenteditable][lang=en-US]");
+  editingHost.focus();
+
+  await new Promise(resolve => maybeOnSpellCheck(editingHost, resolve));
+
+  let editingSession = SpecialPowers.wrap(window).docShell.editingSession;
+  let editor = editingSession.getEditorForWindow(window);
+  let spellchecker = SpecialPowers.Cu.createSpellChecker();
+  spellchecker.setFilterType(spellchecker.FILTERTYPE_NORMAL);
+
+  /* Select "missspelled" in the <div>. */
+  window.getSelection().selectAllChildren(editingHost);
+
+  /* Pass true to InitSpellChecker to spellcheck the current selection of the editor.*/
+  await new Promise(resolve => spellchecker.InitSpellChecker(editor, true, resolve));
+
+  /* InitSpellChecker with enableSelectionChecking=true shouldn't throw any errors. */
+  ok(spellchecker.canSpellCheck());
+});
+</script>
diff --git a/editor/spellchecker/tests/test_suggest.html b/editor/spellchecker/tests/test_suggest.html
new file mode 100644
index 0000000000..b3e35458c7
--- /dev/null
+++ b/editor/spellchecker/tests/test_suggest.html
@@ -0,0 +1,42 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Test for nsIEditorSpellChecfker.sugget</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+
+<div contenteditable id="en-US" lang="en-US">missspelled</div>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+add_task(async function() {
+  await new Promise(resolve => SimpleTest.waitForFocus(resolve));
+
+  let { maybeOnSpellCheck } = SpecialPowers.ChromeUtils.importESModule(
+    "resource://testing-common/AsyncSpellCheckTestHelper.sys.mjs"
+  );
+
+  let element = document.getElementById("en-US");
+  element.focus();
+
+  await new Promise(resolve => maybeOnSpellCheck(element, resolve));
+
+  let editingSession = SpecialPowers.wrap(window).docShell.editingSession;
+  let editor = editingSession.getEditorForWindow(window);
+  let spellchecker = SpecialPowers.Cu.createSpellChecker();
+  spellchecker.setFilterType(spellchecker.FILTERTYPE_NORMAL);
+  await new Promise(resolve => spellchecker.InitSpellChecker(editor, false, resolve));
+
+  let suggestions = await spellchecker.suggest("misspelled", 5);
+  is(suggestions.length, 0, "\"misspelled\" is correct word");
+
+  suggestions = await spellchecker.suggest("missspelled", 5);
+  is(suggestions.length, 5, "\"missspelled\" isn't correct word");
+});
+</script>
+</pre>
+</body>
+</html>