diff --git a/devtools/client/shared/vendor/source-map/lib/array-set.js b/devtools/client/shared/vendor/source-map/lib/array-set.js
index a0f9086c6609..d2ed9cd1353a 100644
--- a/devtools/client/shared/vendor/source-map/lib/array-set.js
+++ b/devtools/client/shared/vendor/source-map/lib/array-set.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2011 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/devtools/client/shared/vendor/source-map/lib/base64-vlq.js b/devtools/client/shared/vendor/source-map/lib/base64-vlq.js
index 450bd03a2408..2daed1eb5ae3 100644
--- a/devtools/client/shared/vendor/source-map/lib/base64-vlq.js
+++ b/devtools/client/shared/vendor/source-map/lib/base64-vlq.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2011 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/devtools/client/shared/vendor/source-map/lib/base64.js b/devtools/client/shared/vendor/source-map/lib/base64.js
index 45ca5b9079eb..939abc8e1e31 100644
--- a/devtools/client/shared/vendor/source-map/lib/base64.js
+++ b/devtools/client/shared/vendor/source-map/lib/base64.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2011 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/devtools/client/shared/vendor/source-map/lib/binary-search.js b/devtools/client/shared/vendor/source-map/lib/binary-search.js
index 6af89f6c8a3f..db65ccd12ea2 100644
--- a/devtools/client/shared/vendor/source-map/lib/binary-search.js
+++ b/devtools/client/shared/vendor/source-map/lib/binary-search.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2011 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/devtools/client/shared/vendor/source-map/lib/mapping-list.js b/devtools/client/shared/vendor/source-map/lib/mapping-list.js
index c9f78e972234..ece3c2ccc1e4 100644
--- a/devtools/client/shared/vendor/source-map/lib/mapping-list.js
+++ b/devtools/client/shared/vendor/source-map/lib/mapping-list.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2014 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/devtools/client/shared/vendor/source-map/lib/source-map-consumer.js b/devtools/client/shared/vendor/source-map/lib/source-map-consumer.js
index 5a59d644addf..7381a668b5b4 100644
--- a/devtools/client/shared/vendor/source-map/lib/source-map-consumer.js
+++ b/devtools/client/shared/vendor/source-map/lib/source-map-consumer.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2011 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/devtools/client/shared/vendor/source-map/lib/source-map-generator.js b/devtools/client/shared/vendor/source-map/lib/source-map-generator.js
index 64541127efdc..847017fac667 100644
--- a/devtools/client/shared/vendor/source-map/lib/source-map-generator.js
+++ b/devtools/client/shared/vendor/source-map/lib/source-map-generator.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2011 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/devtools/client/shared/vendor/source-map/lib/source-node.js b/devtools/client/shared/vendor/source-map/lib/source-node.js
index f6a9758f294f..ecee1ae620e7 100644
--- a/devtools/client/shared/vendor/source-map/lib/source-node.js
+++ b/devtools/client/shared/vendor/source-map/lib/source-node.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2011 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/devtools/client/shared/vendor/source-map/lib/url.js b/devtools/client/shared/vendor/source-map/lib/url.js
index 4c0b8cf1640c..8bb71b6ac19e 100644
--- a/devtools/client/shared/vendor/source-map/lib/url.js
+++ b/devtools/client/shared/vendor/source-map/lib/url.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2011 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/devtools/client/shared/vendor/source-map/lib/util.js b/devtools/client/shared/vendor/source-map/lib/util.js
index e3c84ce743cf..20fe8f6859aa 100644
--- a/devtools/client/shared/vendor/source-map/lib/util.js
+++ b/devtools/client/shared/vendor/source-map/lib/util.js
@@ -1,3 +1,4 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
 /*
  * Copyright 2011 Mozilla Foundation and contributors
  * Licensed under the New BSD license. See LICENSE or:
diff --git a/gfx/cairo/cairo/src/cairo-quartz-font.c b/gfx/cairo/cairo/src/cairo-quartz-font.c
index 48a2e19cf21c..2819ed02a780 100644
--- a/gfx/cairo/cairo/src/cairo-quartz-font.c
+++ b/gfx/cairo/cairo/src/cairo-quartz-font.c
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; indent-tabs-mode: t; tab-width: 8; -*- */
 /* cairo - a vector graphics library with display and print output
  *
  * Copyright � 2008 Mozilla Corporation
diff --git a/gfx/cairo/cairo/src/cairo-quartz-image-surface.c b/gfx/cairo/cairo/src/cairo-quartz-image-surface.c
index 2ba86468d34b..5b229d166293 100644
--- a/gfx/cairo/cairo/src/cairo-quartz-image-surface.c
+++ b/gfx/cairo/cairo/src/cairo-quartz-image-surface.c
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; indent-tabs-mode: t; tab-width: 8; -*- */
 /* cairo - a vector graphics library with display and print output
  *
  * Copyright � 2008 Mozilla Corporation
diff --git a/gfx/cairo/cairo/src/cairo-quartz-surface.c b/gfx/cairo/cairo/src/cairo-quartz-surface.c
index c53864ccfa9b..296e08ba322a 100644
--- a/gfx/cairo/cairo/src/cairo-quartz-surface.c
+++ b/gfx/cairo/cairo/src/cairo-quartz-surface.c
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; indent-tabs-mode: t; tab-width: 8; -*- */
 /* cairo - a vector graphics library with display and print output
  *
  * Copyright � 2006, 2007 Mozilla Corporation
diff --git a/gfx/cairo/libpixman/src/pixman-combine-float.c b/gfx/cairo/libpixman/src/pixman-combine-float.c
index d5f4d2c1337f..cf72fdbe8c64 100644
--- a/gfx/cairo/libpixman/src/pixman-combine-float.c
+++ b/gfx/cairo/libpixman/src/pixman-combine-float.c
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t; -*- */
 /*
  * Copyright © 2010, 2012 Soren Sandmann Pedersen
  * Copyright © 2010, 2012 Red Hat, Inc.
diff --git a/gfx/cairo/libpixman/src/pixman-combine-float.h b/gfx/cairo/libpixman/src/pixman-combine-float.h
index 269faf4ad2c0..09cbbd040fe9 100644
--- a/gfx/cairo/libpixman/src/pixman-combine-float.h
+++ b/gfx/cairo/libpixman/src/pixman-combine-float.h
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t; -*- */
 /*
  * Copyright © 2010, 2012 Soren Sandmann Pedersen
  * Copyright © 2010, 2012 Red Hat, Inc.
diff --git a/gfx/cairo/libpixman/src/pixman-fast-path.c b/gfx/cairo/libpixman/src/pixman-fast-path.c
index 827685884f92..d510cacbf803 100644
--- a/gfx/cairo/libpixman/src/pixman-fast-path.c
+++ b/gfx/cairo/libpixman/src/pixman-fast-path.c
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t; -*- */
 /*
  * Copyright © 2000 SuSE, Inc.
  * Copyright © 2007 Red Hat, Inc.
diff --git a/gfx/cairo/libpixman/src/pixman-inlines.h b/gfx/cairo/libpixman/src/pixman-inlines.h
index e0f08b9322df..f785910f807b 100644
--- a/gfx/cairo/libpixman/src/pixman-inlines.h
+++ b/gfx/cairo/libpixman/src/pixman-inlines.h
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t; -*- */
 /*
  * Copyright © 2000 SuSE, Inc.
  * Copyright © 2007 Red Hat, Inc.
diff --git a/gfx/cairo/libpixman/src/pixman-linear-gradient.c b/gfx/cairo/libpixman/src/pixman-linear-gradient.c
index 579a4ac5fcdd..014b69ceb0fc 100644
--- a/gfx/cairo/libpixman/src/pixman-linear-gradient.c
+++ b/gfx/cairo/libpixman/src/pixman-linear-gradient.c
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t; -*- */
 /*
  * Copyright © 2000 SuSE, Inc.
  * Copyright © 2007 Red Hat, Inc.
diff --git a/gfx/cairo/libpixman/src/pixman-noop.c b/gfx/cairo/libpixman/src/pixman-noop.c
index 86e4f12a1349..e43199bc18ae 100644
--- a/gfx/cairo/libpixman/src/pixman-noop.c
+++ b/gfx/cairo/libpixman/src/pixman-noop.c
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t; -*- */
 /*
  * Copyright © 2011 Red Hat, Inc.
  *
diff --git a/gfx/cairo/libpixman/src/pixman-radial-gradient.c b/gfx/cairo/libpixman/src/pixman-radial-gradient.c
index 4c00c5fefeb1..38e1052f32b9 100644
--- a/gfx/cairo/libpixman/src/pixman-radial-gradient.c
+++ b/gfx/cairo/libpixman/src/pixman-radial-gradient.c
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t; -*- */
 /*
  *
  * Copyright © 2000 Keith Packard, member of The XFree86 Project, Inc.
diff --git a/gfx/cairo/libpixman/src/pixman.c b/gfx/cairo/libpixman/src/pixman.c
index ecc85578798c..1d77f8ef861f 100644
--- a/gfx/cairo/libpixman/src/pixman.c
+++ b/gfx/cairo/libpixman/src/pixman.c
@@ -1,3 +1,4 @@
+/* -*- Mode: c; c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t; -*- */
 /*
  * Copyright © 2000 SuSE, Inc.
  * Copyright © 2007 Red Hat, Inc.
diff --git a/gfx/qcms/qcmsint.h b/gfx/qcms/qcmsint.h
index 173f38153e39..b08fc9490b1f 100644
--- a/gfx/qcms/qcmsint.h
+++ b/gfx/qcms/qcmsint.h
@@ -1,3 +1,4 @@
+/* vim: set ts=8 sw=8 noexpandtab: */
 #ifndef QCMS_INT_H
 #define QCMS_INT_H
 
diff --git a/ipc/chromium/src/third_party/libevent/Vagrantfile b/ipc/chromium/src/third_party/libevent/Vagrantfile
index aeb2c8ca4c42..d275089e2edb 100644
--- a/ipc/chromium/src/third_party/libevent/Vagrantfile
+++ b/ipc/chromium/src/third_party/libevent/Vagrantfile
@@ -1,3 +1,4 @@
+# -*- mode: ruby -*-
 # vi: set ft=ruby :
 
 # DESCRIPTION:
diff --git a/ipc/chromium/src/third_party/libevent/include/event2/visibility.h b/ipc/chromium/src/third_party/libevent/include/event2/visibility.h
index 859571b97cf3..006bbf06d80f 100644
--- a/ipc/chromium/src/third_party/libevent/include/event2/visibility.h
+++ b/ipc/chromium/src/third_party/libevent/include/event2/visibility.h
@@ -1,3 +1,4 @@
+/* -*- Mode: C; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */
 /*
  * Copyright (c) 2007-2012 Niels Provos and Nick Mathewson
  *
diff --git a/js/src/dtoa.c b/js/src/dtoa.c
index f683699ac99c..762d1c17124a 100644
--- a/js/src/dtoa.c
+++ b/js/src/dtoa.c
@@ -1,3 +1,4 @@
+/* -*- Mode: C; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*- */
 /****************************************************************
  *
  * The author of this software is David M. Gay.
diff --git a/js/src/zydis/ZydisAPI.cpp b/js/src/zydis/ZydisAPI.cpp
index b47d74d22615..aef5edc30ac6 100644
--- a/js/src/zydis/ZydisAPI.cpp
+++ b/js/src/zydis/ZydisAPI.cpp
@@ -1,4 +1,6 @@
-/*
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ *
  * Zyan Disassembler Library (Zydis)
  *
  * Original Author : Code taken from examples on zydis github README.md.
diff --git a/js/src/zydis/ZydisAPI.h b/js/src/zydis/ZydisAPI.h
index 52503b160081..ce161580fe09 100644
--- a/js/src/zydis/ZydisAPI.h
+++ b/js/src/zydis/ZydisAPI.h
@@ -1,4 +1,6 @@
-/*
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ *
  * Copyright 2019 Mozilla Foundation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
diff --git a/layout/docs/css-gap-decorations/Overview.bs b/layout/docs/css-gap-decorations/Overview.bs
index ff3a0cc935c3..982ec7dd3e25 100644
--- a/layout/docs/css-gap-decorations/Overview.bs
+++ b/layout/docs/css-gap-decorations/Overview.bs
@@ -1,3 +1,4 @@
+<!-- -*- Mode: HTML; indent-tabs-mode: nil; sgml-basic-offset: 4 -*- -->
 <!--
      Any copyright is dedicated to the Public Domain.
      http://creativecommons.org/publicdomain/zero/1.0/
diff --git a/media/libaom/test/fuzztest/av1_fuzzer.cpp b/media/libaom/test/fuzztest/av1_fuzzer.cpp
index f35dccf11c24..a659446773c7 100644
--- a/media/libaom/test/fuzztest/av1_fuzzer.cpp
+++ b/media/libaom/test/fuzztest/av1_fuzzer.cpp
@@ -1,3 +1,5 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
 /* Copyright 2018 Google Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
diff --git a/other-licenses/bsdiff/bsdiff.c b/other-licenses/bsdiff/bsdiff.c
index d48f707cc93c..eaf902736501 100644
--- a/other-licenses/bsdiff/bsdiff.c
+++ b/other-licenses/bsdiff/bsdiff.c
@@ -1,3 +1,4 @@
+/* vim:set ts=8 sw=8 sts=8 noet: */
 /*
   bsdiff.c -- Binary patch generator.
 
diff --git a/testing/talos/talos/tests/dromaeo/JSON.php b/testing/talos/talos/tests/dromaeo/JSON.php
index 615b03226bc9..8283e7ef7791 100644
--- a/testing/talos/talos/tests/dromaeo/JSON.php
+++ b/testing/talos/talos/tests/dromaeo/JSON.php
@@ -1,4 +1,5 @@
 <?php
+/* vim: set expandtab tabstop=4 shiftwidth=4 softtabstop=4: */
 
 /**
  * Converts to and from JSON format.
diff --git a/toolkit/crashreporter/google-breakpad/src/common/byte_cursor.h b/toolkit/crashreporter/google-breakpad/src/common/byte_cursor.h
index cd718fb47213..accd54e0a414 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/byte_cursor.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/byte_cursor.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf/bytereader.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf/bytereader.h
index 1520ed086d7d..59d430348079 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf/bytereader.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf/bytereader.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf/cfi_assembler.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf/cfi_assembler.h
index 136f135d8e68..bd7354d12753 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf/cfi_assembler.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf/cfi_assembler.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2diehandler.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2diehandler.h
index ba84e6a2dee9..a1e589a863e0 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2diehandler.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2diehandler.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2diehandler_unittest.cc b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2diehandler_unittest.cc
index 72c56b87f59a..db70eb31b9e3 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2diehandler_unittest.cc
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2diehandler_unittest.cc
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2enums.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2enums.h
index e3d555ec2198..4316a89ccd6e 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2enums.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2enums.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2reader.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2reader.h
index c74274995ef0..902d9ef1f422 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2reader.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2reader.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2reader_test_common.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2reader_test_common.h
index 3b01041a108d..e91de90610de 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2reader_test_common.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf/dwarf2reader_test_common.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2012, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf_cfi_to_module.cc b/toolkit/crashreporter/google-breakpad/src/common/dwarf_cfi_to_module.cc
index 2597046749a4..47060f7f3616 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf_cfi_to_module.cc
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf_cfi_to_module.cc
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf_cfi_to_module.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf_cfi_to_module.h
index c6827f089ac4..0d28048d30ec 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf_cfi_to_module.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf_cfi_to_module.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf_cu_to_module.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf_cu_to_module.h
index dc4367a8ed7f..f73a3c933b55 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf_cu_to_module.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf_cu_to_module.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf_line_to_module.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf_line_to_module.h
index 69af20750181..1fdd4cb716fa 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf_line_to_module.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf_line_to_module.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/dwarf_range_list_handler.h b/toolkit/crashreporter/google-breakpad/src/common/dwarf_range_list_handler.h
index 825ed3919aff..bd0996863d92 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/dwarf_range_list_handler.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/dwarf_range_list_handler.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2018 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/language.h b/toolkit/crashreporter/google-breakpad/src/common/language.h
index 1edde98930fc..2d2dbcd9e928 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/language.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/language.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/linux/dump_symbols.h b/toolkit/crashreporter/google-breakpad/src/common/linux/dump_symbols.h
index 5f3d0b942ebf..eaddd8b2ec87 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/linux/dump_symbols.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/linux/dump_symbols.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2011, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/linux/elf_gnu_compat.h b/toolkit/crashreporter/google-breakpad/src/common/linux/elf_gnu_compat.h
index 03f669ea5ab6..0a3dfedb5793 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/linux/elf_gnu_compat.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/linux/elf_gnu_compat.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2013, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/linux/elf_symbols_to_module.cc b/toolkit/crashreporter/google-breakpad/src/common/linux/elf_symbols_to_module.cc
index acdd7d699b88..562875e11b5f 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/linux/elf_symbols_to_module.cc
+++ b/toolkit/crashreporter/google-breakpad/src/common/linux/elf_symbols_to_module.cc
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2011 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
diff --git a/toolkit/crashreporter/google-breakpad/src/common/linux/elf_symbols_to_module.h b/toolkit/crashreporter/google-breakpad/src/common/linux/elf_symbols_to_module.h
index ba029aac67a2..2e7c097151cd 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/linux/elf_symbols_to_module.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/linux/elf_symbols_to_module.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2011 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
diff --git a/toolkit/crashreporter/google-breakpad/src/common/linux/symbol_upload.h b/toolkit/crashreporter/google-breakpad/src/common/linux/symbol_upload.h
index bc8406828af9..9033152bf287 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/linux/symbol_upload.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/linux/symbol_upload.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2011 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/linux/synth_elf.h b/toolkit/crashreporter/google-breakpad/src/common/linux/synth_elf.h
index 188e6416054c..1d2a20ca22b4 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/linux/synth_elf.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/linux/synth_elf.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2011, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/mac/byteswap.h b/toolkit/crashreporter/google-breakpad/src/common/mac/byteswap.h
index 288ccd26b7d3..b7bbc0b95bbd 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/mac/byteswap.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/mac/byteswap.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/mac/dump_syms.cc b/toolkit/crashreporter/google-breakpad/src/common/mac/dump_syms.cc
index 30a2992df767..3c48f23528f3 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/mac/dump_syms.cc
+++ b/toolkit/crashreporter/google-breakpad/src/common/mac/dump_syms.cc
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2011, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/mac/dump_syms.h b/toolkit/crashreporter/google-breakpad/src/common/mac/dump_syms.h
index c5a97ad8920d..1e57f86ddd96 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/mac/dump_syms.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/mac/dump_syms.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2011, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/mac/macho_reader.h b/toolkit/crashreporter/google-breakpad/src/common/mac/macho_reader.h
index 9f54c3b12854..145d17d1f2a7 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/mac/macho_reader.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/mac/macho_reader.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/module.h b/toolkit/crashreporter/google-breakpad/src/common/module.h
index f878f49bc22e..37758605260e 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/module.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/module.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/stabs_reader.h b/toolkit/crashreporter/google-breakpad/src/common/stabs_reader.h
index 861d84c735cc..98ee2dd53b40 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/stabs_reader.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/stabs_reader.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
diff --git a/toolkit/crashreporter/google-breakpad/src/common/stabs_to_module.h b/toolkit/crashreporter/google-breakpad/src/common/stabs_to_module.h
index 4453a01367a6..5e04fa79279e 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/stabs_to_module.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/stabs_to_module.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/symbol_data.h b/toolkit/crashreporter/google-breakpad/src/common/symbol_data.h
index 7a0de315edd4..2cf15a855db9 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/symbol_data.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/symbol_data.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2013 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/test_assembler.h b/toolkit/crashreporter/google-breakpad/src/common/test_assembler.h
index 4abdf1e182b6..373dbebacd00 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/test_assembler.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/test_assembler.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/common/testdata/func-line-pairing.h b/toolkit/crashreporter/google-breakpad/src/common/testdata/func-line-pairing.h
index 1a2bf25b82a8..05538f961b5b 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/testdata/func-line-pairing.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/testdata/func-line-pairing.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Test data for pairing functions and lines.
 // 
 // For a pair of functions that are adjacent (10,20),(20,25) and a
diff --git a/toolkit/crashreporter/google-breakpad/src/common/using_std_string.h b/toolkit/crashreporter/google-breakpad/src/common/using_std_string.h
index 884def533f7c..13c1da59ccb5 100644
--- a/toolkit/crashreporter/google-breakpad/src/common/using_std_string.h
+++ b/toolkit/crashreporter/google-breakpad/src/common/using_std_string.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2012, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/source_line_resolver_interface.h b/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/source_line_resolver_interface.h
index c147f6e3f213..a694bf2ea113 100644
--- a/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/source_line_resolver_interface.h
+++ b/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/source_line_resolver_interface.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/stack_frame_cpu.h b/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/stack_frame_cpu.h
index b5b5d07fa1dd..dc5d8ae67391 100644
--- a/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/stack_frame_cpu.h
+++ b/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/stack_frame_cpu.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/stack_frame_symbolizer.h b/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/stack_frame_symbolizer.h
index c38c0d4db71a..0bbaae0a3638 100644
--- a/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/stack_frame_symbolizer.h
+++ b/toolkit/crashreporter/google-breakpad/src/google_breakpad/processor/stack_frame_symbolizer.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2012 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/cfi_frame_info-inl.h b/toolkit/crashreporter/google-breakpad/src/processor/cfi_frame_info-inl.h
index d94eda183a28..7e7af0af93af 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/cfi_frame_info-inl.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/cfi_frame_info-inl.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/cfi_frame_info.h b/toolkit/crashreporter/google-breakpad/src/processor/cfi_frame_info.h
index e6ef798eb929..90a1b3d74a9c 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/cfi_frame_info.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/cfi_frame_info.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/postfix_evaluator-inl.h b/toolkit/crashreporter/google-breakpad/src/processor/postfix_evaluator-inl.h
index 02d1384f25cf..d7dbeac20516 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/postfix_evaluator-inl.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/postfix_evaluator-inl.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/postfix_evaluator.h b/toolkit/crashreporter/google-breakpad/src/processor/postfix_evaluator.h
index 8dfd2e1eaaa8..94b66190d5dc 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/postfix_evaluator.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/postfix_evaluator.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_arm.h b/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_arm.h
index 8d8244a3f58e..9081a40cd0a6 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_arm.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_arm.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_arm64.h b/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_arm64.h
index e9e5044a0cda..3f9e4f19c4e3 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_arm64.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_arm64.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2013 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_unittest_utils.h b/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_unittest_utils.h
index 3ea22a000677..3a92a5ea7a78 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_unittest_utils.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_unittest_utils.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_x86.h b/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_x86.h
index 551aa3c4ea8a..0659a13bf4cf 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_x86.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/stackwalker_x86.h
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2010 Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/synth_minidump.h b/toolkit/crashreporter/google-breakpad/src/processor/synth_minidump.h
index 491b1af9d074..8f49cfff22a9 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/synth_minidump.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/synth_minidump.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
diff --git a/toolkit/crashreporter/google-breakpad/src/processor/synth_minidump_unittest_data.h b/toolkit/crashreporter/google-breakpad/src/processor/synth_minidump_unittest_data.h
index e79e561b8bff..3403372e6c2c 100644
--- a/toolkit/crashreporter/google-breakpad/src/processor/synth_minidump_unittest_data.h
+++ b/toolkit/crashreporter/google-breakpad/src/processor/synth_minidump_unittest_data.h
@@ -1,3 +1,5 @@
+// -*- mode: C++ -*-
+
 // Not copyrightable: random test data.
 // synth_minidump_unittest_data.h: verbose test data for SynthMinidump tests.
 
diff --git a/toolkit/crashreporter/google-breakpad/src/tools/mac/dump_syms/dump_syms_tool.cc b/toolkit/crashreporter/google-breakpad/src/tools/mac/dump_syms/dump_syms_tool.cc
index 714e2779f1d7..6f68457b4c16 100644
--- a/toolkit/crashreporter/google-breakpad/src/tools/mac/dump_syms/dump_syms_tool.cc
+++ b/toolkit/crashreporter/google-breakpad/src/tools/mac/dump_syms/dump_syms_tool.cc
@@ -1,3 +1,5 @@
+// -*- mode: c++ -*-
+
 // Copyright (c) 2011, Google Inc.
 // All rights reserved.
 //