--- a/extensions/spellcheck/hunspell/glue/moz.build
+++ b/extensions/spellcheck/hunspell/glue/moz.build
@@ -2,16 +2,17 @@
 # vim: set filetype=python:
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 UNIFIED_SOURCES += [
     'mozHunspell.cpp',
     'mozHunspellDirProvider.cpp',
+    'mozHunspellFileMgr.cpp',
     'RemoteSpellCheckEngineChild.cpp',
     'RemoteSpellCheckEngineParent.cpp',
 ]
 
 FINAL_LIBRARY = 'xul'
 
 if CONFIG['MOZ_SYSTEM_HUNSPELL']:
     CXXFLAGS += CONFIG['MOZ_HUNSPELL_CFLAGS']

new file mode 100644
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspellFileMgr.cpp
@@ -0,0 +1,75 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozHunspellFileMgr.h"
+
+#include "mozilla/Unused.h"
+#include "nsContentUtils.h"
+#include "nsILoadInfo.h"
+#include "nsNetUtil.h"
+#include "nsXPCOM.h"
+
+using namespace mozilla;
+
+FileMgr::FileMgr(const char* aFilename, const char* aKey)
+{
+  auto result = Open(nsDependentCString(aFilename));
+  NS_WARNING_ASSERTION(result.isOk(), "Failed to open Hunspell file");
+}
+
+Result<Ok, nsresult>
+FileMgr::Open(const nsACString& aPath)
+{
+  nsCOMPtr<nsIURI> uri;
+
+  nsresult rv = NS_NewURI(getter_AddRefs(uri), aPath);
+  if (NS_FAILED(rv)) {
+    nsCOMPtr<nsIFile> file;
+    MOZ_TRY(NS_NewNativeLocalFile(aPath, false, getter_AddRefs(file)));
+    MOZ_TRY(NS_NewFileURI(getter_AddRefs(uri), file));
+  }
+
+  nsCOMPtr<nsIChannel> channel;
+  MOZ_TRY(NS_NewChannel(
+    getter_AddRefs(channel),
+    uri,
+    nsContentUtils::GetSystemPrincipal(),
+    nsILoadInfo::SEC_REQUIRE_SAME_ORIGIN_DATA_INHERITS,
+    nsIContentPolicy::TYPE_OTHER));
+
+  MOZ_TRY(channel->Open2(getter_AddRefs(mStream)));
+  return Ok();
+}
+
+Result<Ok, nsresult>
+FileMgr::ReadLine(nsACString& aLine)
+{
+  if (!mStream) {
+    return Err(NS_ERROR_NOT_INITIALIZED);
+  }
+
+  bool ok;
+  MOZ_TRY(NS_ReadLine(mStream.get(), &mLineBuffer, aLine, &ok));
+  if (!ok) {
+    mStream = nullptr;
+  }
+
+  mLineNum++;
+  return Ok();
+}
+
+bool
+FileMgr::getline(std::string& aResult)
+{
+  nsAutoCString line;
+  auto res = ReadLine(line);
+  if (res.isErr()) {
+    return false;
+  }
+
+  aResult.assign(line.BeginReading(), line.Length());
+  return true;
+}

new file mode 100644
--- /dev/null
+++ b/extensions/spellcheck/hunspell/glue/mozHunspellFileMgr.h
@@ -0,0 +1,47 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozHunspellFileMgr_h
+#define mozHunspellFileMgr_h
+
+#include <string>
+
+#include "mozilla/Result.h"
+#include "mozilla/ResultExtensions.h"
+#include "nsIInputStream.h"
+#include "nsReadLine.h"
+
+// Note: This class name and lack of namespacing terrible, but are necessary
+// for Hunspell compatibility.
+class FileMgr final
+{
+public:
+  /**
+   * aFilename may be the native filesystem path or local file/jar URI for the
+   * file to load.
+   *
+   * aKey is the decription key for encrypted Hunzip files, and is
+   * unsupported. The argument is there solely for compatibility.
+   */
+  FileMgr(const char* aFilename, const char* aKey = nullptr);
+  ~FileMgr() = default;
+
+  // Note: The nonstandard naming conventions of these methods are necessary for
+  // Hunspell compatibility.
+  bool getline(std::string& aLine);
+  int getlinenum() const { return mLineNum; }
+
+private:
+  mozilla::Result<mozilla::Ok, nsresult> Open(const nsACString& aPath);
+
+  mozilla::Result<mozilla::Ok, nsresult> ReadLine(nsACString& aLine);
+
+  int mLineNum = 0;
+  nsCOMPtr<nsIInputStream> mStream;
+  nsLineBuffer<char> mLineBuffer;
+};
+
+#endif // mozHunspellFileMgr_h

deleted file mode 100644
--- a/extensions/spellcheck/hunspell/src/filemgr.cxx
+++ /dev/null
@@ -1,117 +0,0 @@
-/* ***** BEGIN LICENSE BLOCK *****
- * Version: MPL 1.1/GPL 2.0/LGPL 2.1
- *
- * Copyright (C) 2002-2017 Németh László
- *
- * The contents of this file are subject to the Mozilla Public License Version
- * 1.1 (the "License"); you may not use this file except in compliance with
- * the License. You may obtain a copy of the License at
- * http://www.mozilla.org/MPL/
- *
- * Software distributed under the License is distributed on an "AS IS" basis,
- * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
- * for the specific language governing rights and limitations under the
- * License.
- *
- * Hunspell is based on MySpell which is Copyright (C) 2002 Kevin Hendricks.
- *
- * Contributor(s): David Einstein, Davide Prina, Giuseppe Modugno,
- * Gianluca Turconi, Simon Brouwer, Noll János, Bíró Árpád,
- * Goldman Eleonóra, Sarlós Tamás, Bencsáth Boldizsár, Halácsy Péter,
- * Dvornik László, Gefferth András, Nagy Viktor, Varga Dániel, Chris Halls,
- * Rene Engelhard, Bram Moolenaar, Dafydd Jones, Harri Pitkänen
- *
- * Alternatively, the contents of this file may be used under the terms of
- * either the GNU General Public License Version 2 or later (the "GPL"), or
- * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
- * in which case the provisions of the GPL or the LGPL are applicable instead
- * of those above. If you wish to allow use of your version of this file only
- * under the terms of either the GPL or the LGPL, and not to allow others to
- * use your version of this file under the terms of the MPL, indicate your
- * decision by deleting the provisions above and replace them with the notice
- * and other provisions required by the GPL or the LGPL. If you do not delete
- * the provisions above, a recipient may use your version of this file under
- * the terms of any one of the MPL, the GPL or the LGPL.
- *
- * ***** END LICENSE BLOCK ***** */
-/*
- * Copyright 2002 Kevin B. Hendricks, Stratford, Ontario, Canada
- * And Contributors.  All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- *
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- *
- * 3. All modifications to the source code must be clearly marked as
- *    such.  Binary redistributions based on modified source code
- *    must be clearly marked as modified versions in the documentation
- *    and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY KEVIN B. HENDRICKS AND CONTRIBUTORS
- * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
- * KEVIN B. HENDRICKS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
- * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <stdlib.h>
-#include <string.h>
-#include <stdio.h>
-
-#include "filemgr.hxx"
-#include "csutil.hxx"
-
-int FileMgr::fail(const char* err, const char* par) {
-  fprintf(stderr, err, par);
-  return -1;
-}
-
-FileMgr::FileMgr(const char* file, const char* key) : hin(NULL), linenum(0) {
-  in[0] = '\0';
-
-  myopen(fin, file, std::ios_base::in);
-  if (!fin.is_open()) {
-    // check hzipped file
-    std::string st(file);
-    st.append(HZIP_EXTENSION);
-    hin = new Hunzip(st.c_str(), key);
-  }
-  if (!fin.is_open() && !hin->is_open())
-    fail(MSG_OPEN, file);
-}
-
-FileMgr::~FileMgr() {
-  delete hin;
-}
-
-bool FileMgr::getline(std::string& dest) {
-  bool ret = false;
-  ++linenum;
-  if (fin.is_open()) {
-    ret = static_cast<bool>(std::getline(fin, dest));
-  } else if (hin->is_open()) {
-    ret = hin->getline(dest);
-  }
-  if (!ret) {
-    --linenum;
-  }
-  return ret;
-}
-
-int FileMgr::getlinenum() {
-  return linenum;
-}

--- a/extensions/spellcheck/hunspell/src/filemgr.hxx
+++ b/extensions/spellcheck/hunspell/src/filemgr.hxx
@@ -67,32 +67,11 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 /* file manager class - read lines of files [filename] OR [filename.hz] */
 #ifndef FILEMGR_HXX_
 #define FILEMGR_HXX_
 
-#include "hunzip.hxx"
-#include <stdio.h>
-#include <string>
-#include <fstream>
-
-class FileMgr {
- private:
-  FileMgr(const FileMgr&);
-  FileMgr& operator=(const FileMgr&);
+#include "mozHunspellFileMgr.h"
 
- protected:
-  std::ifstream fin;
-  Hunzip* hin;
-  char in[BUFSIZE + 50];  // input buffer
-  int fail(const char* err, const char* par);
-  int linenum;
-
- public:
-  FileMgr(const char* filename, const char* key = NULL);
-  ~FileMgr();
-  bool getline(std::string&);
-  int getlinenum();
-};
 #endif

--- a/extensions/spellcheck/hunspell/src/moz.build
+++ b/extensions/spellcheck/hunspell/src/moz.build
@@ -3,20 +3,18 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 UNIFIED_SOURCES += [
     'affentry.cxx',
     'affixmgr.cxx',
     'csutil.cxx',
-    'filemgr.cxx',
     'hashmgr.cxx',
     'hunspell.cxx',
-    'hunzip.cxx',
     'phonet.cxx',
     'replist.cxx',
     'suggestmgr.cxx',
 ]
 
 # This variable is referenced in configure.in.  Make sure to change that file
 # too if you need to change this variable.
 DEFINES['HUNSPELL_STATIC'] = True