diff --git a/.hgignore b/.hgignore
index 33a123a1b3f4..aa8ee10d9fd8 100644
--- a/.hgignore
+++ b/.hgignore
@@ -267,3 +267,8 @@ toolkit/components/certviewer/content/package-lock.json
 ^tools/esmify/jscodeshift.cmd
 ^tools/esmify/jscodeshift.ps1
 ^tools/esmify/package-lock.json
+
+# Ignore support files for en-US dictionary updates
+^extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/scowl
+^extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/support_files/
+^extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/*en_US-mozilla*
diff --git a/extensions/spellcheck/docs/index.rst b/extensions/spellcheck/docs/index.rst
index aeea5960d880..2f83dc156e83 100644
--- a/extensions/spellcheck/docs/index.rst
+++ b/extensions/spellcheck/docs/index.rst
@@ -30,9 +30,9 @@ This section describes the process for adding a word to the dictionary:
 #. There’s a special script used for editing dictionaries. The script
    only works if you have the environment variable ``EDITOR`` set to the
    executable of an editor program; if you don’t have it set, you can use
-   ``EDITOR=vim sh edit-dictionary`` to edit using ``vim`` (or you can
+   ``EDITOR=vim sh edit-dictionary.sh`` to edit using ``vim`` (or you can
    substitute it with another editor), or you can just type
-   ``sh edit-dictionary`` if you have an ``EDITOR`` already specified.
+   ``sh edit-dictionary.sh`` if you have an ``EDITOR`` already specified.
 #. Add and remove words in the dictionary file, then quit the editor.
 #. Build Firefox and test your updated dictionary. Once you’re
    satisfied, use the process described in :ref:`write_a_patch` to create a
@@ -59,13 +59,13 @@ The working directory for this process is
 #. Download the latest version of the dictionary from `SCOWL`_ homepage or
    `SourceForce`_ as a tarball (tag.gz) and unpack it in the working directory.
    Rename the resulting folder from ``scowl-YYYY.MM.DD`` to ``scowl``.
-#. Run the script ``sh make-new-dict`` to generate a new dictionary and make
+#. Run the script ``sh make-new-dict.sh`` to generate a new dictionary and make
    sure it runs without any errors. For more details on this script, see the
-   `make-new-dict`_ section.
+   `make-new-dict.sh`_ section.
 #. Do a sanity check on the resulting dictionary file ``en_US-mozilla.dic``. For
    example, make sure that the size is about the same as the original dictionary
    (or slightly larger).
-#. If everything looks correct, use ``sh install-new-dict`` to copy the
+#. If everything looks correct, use ``sh install-new-dict.sh`` to copy the
    generated file in the right position and use the process described in
    :ref:`write_a_patch` to create a patch.
 
@@ -76,7 +76,7 @@ mozilla-exclusions.txt
 ----------------------
 
 ``mozilla-exclusions.txt`` is used to explicitly exclude some words from
-suggestions. The ``make-new-dict`` script will add them to the dictionary file
+suggestions. The ``make-new-dict.sh`` script will add them to the dictionary file
 with the ``/!`` flag.
 
 Terms should be added to this file with exactly the same format used in the .dic
@@ -101,10 +101,10 @@ treats ISO-8859-1 files as binary and won’t display a diff when updating them.
 Info about the included scripts
 ===============================
 
-make-new-dict
--------------
+make-new-dict.sh
+----------------
 
-The dictionary upgrade scripts ``make-new-dict`` works by expanding (i.e.
+The dictionary upgrade scripts ``make-new-dict.sh`` works by expanding (i.e.
 “unmunching”) the affix compression dictionaries to create wordlists and
 use those to generate a new dictionary.
 
@@ -136,17 +136,17 @@ following order:
   included in ``5-mozilla-specific.txt`` should be removed from this list.
 
 The new dictionary is available as ``en_US-mozilla.dic`` and should be copied
-over using the ``install-new-dict`` script.
+over using the ``install-new-dict.sh`` script.
 
-install-new-dict
-----------------
+install-new-dict.sh
+-------------------
 
 The script:
 
 * Creates a copy of ``orig`` as ``support_files/orig-bk`` and copies the new
   upstream version to ``orig``.
 * Copies the existing Mozilla dictionary in ``support_files/mozilla-bk``.
-* Converts the dictionary (.dic) generated by ``make-new-dict`` from UTF-8 to
+* Converts the dictionary (.dic) generated by ``make-new-dict.sh`` from UTF-8 to
   ISO-8859-1 and moves it to the parent folder.
 * Sets the affix file (.aff) to use ``ISO8859-1`` as ``SET`` instead of the
   original ``UTF-8``, removes ``ICONV`` patterns (input conversion tables).
diff --git a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/edit-dictionary b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/edit-dictionary
deleted file mode 100755
index ad77e47fd12a..000000000000
--- a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/edit-dictionary
+++ /dev/null
@@ -1,31 +0,0 @@
-#!/bin/sh
-# 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/.
-
-#
-# edit-dictionary
-
-set -e
-
-if [ -z "$EDITOR" ]; then
-  echo 'Need to set the $EDITOR environment variable to your favorite editor!'
-  exit 1
-fi
-
-# Strip the first line that contains the count
-tail -n +2 ../en-US.dic > en-US.stripped
-
-# Open the patched hunspell editor and let the user edit it
-echo "Now the dictionary is going to be opened for you to edit.  When you're done, just quit the editor"
-echo -n "Press Enter to begin."
-read foo
-$EDITOR en-US.stripped
-
-# Add back the line count
-wc -l < en-US.stripped | tr -d '[:blank:]' > en-US.dic
-LC_ALL=C sort en-US.stripped >> en-US.dic
-
-# Clean up
-rm -f en-US.stripped
-
diff --git a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/edit-dictionary.sh b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/edit-dictionary.sh
new file mode 100755
index 000000000000..7687f8e72789
--- /dev/null
+++ b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/edit-dictionary.sh
@@ -0,0 +1,37 @@
+#! /usr/bin/env sh
+
+# 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/.
+
+set -e
+
+if [ -z "$EDITOR" ]; then
+  echo 'Need to set the $EDITOR environment variable to your favorite editor.'
+  exit 1
+fi
+
+# Copy the current en-US dictionary and strip the first line that contains
+# the count.
+tail -n +2 ../en-US.dic > en-US.stripped
+
+# Convert the file to UTF-8
+iconv -f iso-8859-1 -t utf-8 en-US.stripped > en-US.utf8
+rm en-US.stripped
+
+# Open the hunspell dictionary and let the user edit it
+echo "Now the dictionary is going to be opened for you to edit. Quit the editor to finish editing."
+echo "Press Enter to begin."
+read foo
+$EDITOR en-US.utf8
+
+# Add back the line count and sort the lines
+wc -l < en-US.utf8 | tr -d '[:blank:]' > en-US.dic
+LC_ALL=C sort en-US.utf8 >> en-US.dic
+rm -f en-US.utf8
+
+# Convert back to ISO-8859-1
+iconv -f utf-8 -t iso-8859-1 en-US.dic > ../en-US.dic
+
+# Keep a copy of the UTF-8 file in /utf8
+mv en-US.dic utf8/en-US-utf8.dic
diff --git a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/install-new-dict b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/install-new-dict
deleted file mode 100755
index 24492cad22c2..000000000000
--- a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/install-new-dict
+++ /dev/null
@@ -1,39 +0,0 @@
-#!/bin/sh
-
-#
-# This script copies the new dictionary created by make-new-dict in
-# place.
-#
-
-set -e
-
-WKDIR="`pwd`"
-export SCOWL="$WKDIR/scowl/"
-SPELLER="$SCOWL/speller"
-
-set -x
-
-if [ -e orig-bk ]; then echo "$0: directory 'orig-bk' exists." 1>&2 ; exit 0; fi
-mv orig orig-bk
-mkdir orig
-cp $SPELLER/en_US-custom.dic $SPELLER/en_US-custom.aff $SPELLER/README_en_US-custom.txt orig
-
-mkdir mozilla-bk
-mv ../en-US.dic ../en-US.aff ../README_en_US.txt mozilla-bk
-
-# Convert the affix file to ISO8859-1
-sed -i=bak -e '/^ICONV/d' -e 's/^SET UTF-8$/SET ISO8859-1/' en_US-mozilla.aff
-
-# Convert the dictionary to ISO8859-1
-mv en_US-mozilla.dic en_US-mozilla-utf8.dic
-iconv -f utf-8 -t iso-8859-1 < en_US-mozilla-utf8.dic > en_US-mozilla.dic
-
-cp en_US-mozilla.aff ../en-US.aff
-cp en_US-mozilla.dic ../en-US.dic
-cp README_en_US-mozilla.txt ../README_en_US.txt
-
-set +x
-
-echo "New dictionary copied into place.  Please commit the changes."
-
-
diff --git a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/install-new-dict.sh b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/install-new-dict.sh
new file mode 100755
index 000000000000..26ce06dec269
--- /dev/null
+++ b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/install-new-dict.sh
@@ -0,0 +1,41 @@
+#! /usr/bin/env sh
+
+# 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/.
+
+# This script copies the new dictionary created by make-new-dict in
+# place.
+
+set -e
+
+WKDIR="`pwd`"
+export SCOWL="$WKDIR/scowl/"
+SUPPORT_DIR="$WKDIR/support_files/"
+SPELLER="$SCOWL/speller"
+
+if [ -e "$SUPPORT_DIR/orig-bk" ]; then
+    echo "$0: directory '$SUPPORT_DIR/orig-bk' exists." 1>&2
+    exit 0
+fi
+
+mv orig "$SUPPORT_DIR/orig-bk"
+mkdir orig
+cp $SPELLER/en_US-custom.dic $SPELLER/en_US-custom.aff $SPELLER/README_en_US-custom.txt orig
+
+mkdir "$SUPPORT_DIR/mozilla-bk"
+mv ../en-US.dic ../en-US.aff ../README_en_US.txt "$SUPPORT_DIR/mozilla-bk"
+
+# Convert the affix file to ISO-8859-1
+cp en_US-mozilla.aff utf8/en-US-utf8.aff
+sed -i "" -e '/^ICONV/d' -e 's/^SET UTF-8$/SET ISO8859-1/' en_US-mozilla.aff
+
+# Convert the dictionary to ISO-8859-1
+mv en_US-mozilla.dic utf8/en-US-utf8.dic
+iconv -f utf-8 -t iso-8859-1 < utf8/en-US-utf8.dic > en_US-mozilla.dic
+
+cp en_US-mozilla.aff ../en-US.aff
+cp en_US-mozilla.dic ../en-US.dic
+mv README_en_US-mozilla.txt ../README_en_US.txt
+
+echo "New dictionary copied into place. Please commit the changes."
diff --git a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/make-new-dict b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/make-new-dict
deleted file mode 100755
index 012b9154e257..000000000000
--- a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/make-new-dict
+++ /dev/null
@@ -1,69 +0,0 @@
-#!/bin/sh
-
-#
-# This script creates a new dictionary by expanding the original,
-# Mozilla's, and the upstream dictionary to remove affix flags and
-# then doing the wordlist equivalent of diff3 to create a new
-# dictionary.
-#
-# The files 2-mozilla-add and 2-mozilla-rem contain words added and
-# removed, receptively in the Mozilla dictionary.  The final
-# dictionary will be in hunspell-en_US-mozilla.zip.
-#
-
-set -e
-
-export LANG=C
-export LC_ALL=C
-export LC_CTYPE=C
-export LC_COLLATE=C
-
-WKDIR="`pwd`"
-
-export SCOWL="$WKDIR/scowl/"
-
-ORIG="$WKDIR/orig/"
-SPELLER="$SCOWL/speller"
-
-expand() {
-  grep -v '^[0-9]\+$' | $SPELLER/munch-list expand $1 | sort -u
-}
-
-cd $SPELLER
-MK_LIST="../mk-list -v1 --accents=both en_US 60"
-cat <<EOF > params.txt
-With Input Command: $MK_LIST
-EOF
-# note: output of make-hunspell-dict is utf-8
-$MK_LIST | ./make-hunspell-dict -one en_US-custom params.txt > ./make-hunspell-dict.log
-cd $WKDIR
-
-# Note: Input and output of "expand" is always iso-8859-1.
-#       All expanded word list files are thus in iso-8859-1.
-
-expand $SPELLER/en.aff < $SPELLER/en.dic.supp > 0-special # input: ASCII
-
-# input in utf-8, expand expects iso-8859-1 so use iconv
-iconv -f utf-8 -t iso-8859-1 $ORIG/en_US-custom.dic | expand $SPELLER/en_US-custom.aff > 1-base.txt
-
-expand ../en-US.aff < ../en-US.dic > 2-mozilla.txt # input: iso-8850-1
-
-# input in utf-8, expand expects iso-8859-1 so use iconv
-iconv -f utf-8 -t iso-8859-1 $SPELLER/en_US-custom.dic | expand $SPELLER/en_US-custom.aff > 3-upstream.txt 
-
-comm -23 1-base.txt 2-mozilla.txt > 2-mozilla-rem
-comm -13 1-base.txt 2-mozilla.txt > 2-mozilla-add
-comm -23 3-upstream.txt 2-mozilla-rem | cat - 2-mozilla-add | sort -u > 4-patched.txt
-
-# note: output of make-hunspell-dict is utf-8
-cat 4-patched.txt | comm -23 - 0-special | $SPELLER/make-hunspell-dict -one en_US-mozilla /dev/null
-
-# sanity check should yield identical results
-#comm -23 1-base.txt 3-upstream.txt > 3-upstream-rem
-#comm -13 1-base.txt 3-upstream.txt > 3-upstream-add
-#comm -23 2-mozilla.txt 3-upstream-rem | cat - 3-upstream-add | sort -u > 4-patched-v2.txt
-
-expand ../en-US.aff < mozilla-specific.txt > 5-mozilla-specific
-
-comm -12 3-upstream.txt 2-mozilla-rem > 5-mozilla-removed
-comm -13 3-upstream.txt 2-mozilla-add > 5-mozilla-added
diff --git a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/make-new-dict.sh b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/make-new-dict.sh
new file mode 100755
index 000000000000..1a190e8c5b10
--- /dev/null
+++ b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/make-new-dict.sh
@@ -0,0 +1,102 @@
+#! /usr/bin/env sh
+
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# This script creates a new dictionary by expanding the original,
+# Mozilla's, and the upstream dictionary to remove affix flags and
+# then doing the wordlist equivalent of diff3 to create a new
+# dictionary.
+#
+# The files 2-mozilla-add and 2-mozilla-rem contain words added and
+# removed, respectively in the Mozilla dictionary. The final
+# dictionary will be in hunspell-en_US-mozilla.zip.
+
+set -e
+
+export LANG=C
+export LC_ALL=C
+export LC_CTYPE=C
+export LC_COLLATE=C
+
+WKDIR="`pwd`"
+
+export SCOWL="$WKDIR/scowl/"
+
+ORIG="$WKDIR/orig/"
+SUPPORT_DIR="$WKDIR/support_files/"
+SPELLER="$SCOWL/speller"
+
+expand() {
+  grep -v '^[0-9]\+$' | $SPELLER/munch-list expand $1 | sort -u
+}
+
+mkdir -p $SUPPORT_DIR
+cd $SPELLER
+MK_LIST="../mk-list -v1 --accents=both en_US 60"
+cat <<EOF > params.txt
+With Input Command: $MK_LIST
+EOF
+# Note: the output of make-hunspell-dict is UTF-8
+$MK_LIST | ./make-hunspell-dict -one en_US-custom params.txt > ./make-hunspell-dict.log
+cd $WKDIR
+
+# Note: Input and output of "expand" is always ISO-8859-1.
+#       All expanded word list files are thus in ISO-8859-1.
+expand $SPELLER/en.aff < $SPELLER/en.dic.supp > $SUPPORT_DIR/0-special.txt
+
+# Input is UTF-8, expand expects ISO-8859-1 so use iconv
+iconv -f utf-8 -t iso-8859-1 $ORIG/en_US-custom.dic | expand $ORIG/en_US-custom.aff > $SUPPORT_DIR/1-base.txt
+
+# The existing Mozilla dictionary is already in ISO-8859-1
+expand ../en-US.aff < ../en-US.dic > $SUPPORT_DIR/2-mozilla.txt
+
+# Input is UTF-8, expand expects ISO-8859-1 so use iconv
+iconv -f utf-8 -t iso-8859-1 $SPELLER/en_US-custom.dic | expand $SPELLER/en_US-custom.aff > $SUPPORT_DIR/3-upstream.txt
+
+# Suppress common lines and lines only in the 2nd file, leaving words that are
+# only available in the 1st file (SCOWL), i.e. were removed by Mozilla.
+comm -23 $SUPPORT_DIR/1-base.txt $SUPPORT_DIR/2-mozilla.txt > $SUPPORT_DIR/2-mozilla-removed.txt
+
+# Suppress common lines and lines only in the 1st file, leaving words that are
+# only available in the 2nd file (current Mozilla dictionary), i.e. were added
+# by Mozilla.
+comm -13 $SUPPORT_DIR/1-base.txt $SUPPORT_DIR/2-mozilla.txt > $SUPPORT_DIR/2-mozilla-added.txt
+
+# Suppress common lines and lines only in the 2nd file, leaving words that are
+# only available in the 1st file (words from the new upstream SCOWL dictionary).
+# The result is upstream, minus the words removed, plus the words added.
+comm -23 $SUPPORT_DIR/3-upstream.txt $SUPPORT_DIR/2-mozilla-removed.txt | cat - $SUPPORT_DIR/2-mozilla-added.txt | sort -u > $SUPPORT_DIR/4-patched.txt
+
+# Note: the output of make-hunspell-dict is UTF-8
+cat $SUPPORT_DIR/4-patched.txt | comm -23 - $SUPPORT_DIR/0-special.txt | $SPELLER/make-hunspell-dict -one en_US-mozilla /dev/null
+
+# Exclude specific words from suggestions
+while IFS= read -r line
+do
+  # If the string already contains an affix, just add !, otherwise add /!
+  if [[ "$line" == *"/"* ]]; then
+    sed -i "" "s|^$line$|$line!|" en_US-mozilla.dic
+  else
+    sed -i "" "s|^$line$|$line/!|" en_US-mozilla.dic
+  fi
+done < "mozilla-exclusions.txt"
+
+# Sanity check should yield identical results
+#comm -23 $SUPPORT_DIR/1-base.txt $SUPPORT_DIR/3-upstream.txt > $SUPPORT_DIR/3-upstream-remover.txt
+#comm -13 $SUPPORT_DIR/1-base.txt $SUPPORT_DIR/3-upstream.txt > $SUPPORT_DIR/3-upstream-added.txt
+#comm -23 $SUPPORT_DIR/2-mozilla.txt $SUPPORT_DIR/3-upstream-removed.txt | cat - $SUPPORT_DIR/3-upstream-added.txt | sort -u > $SUPPORT_DIR/4-patched-v2.txt
+
+expand ../en-US.aff < mozilla-specific.txt > 5-mozilla-specific.txt
+
+# Update Mozilla removed and added wordlists based on the new upstream
+# dictionary, save them as UTF-8 and not ISO-8951-1
+comm -12 $SUPPORT_DIR/3-upstream.txt $SUPPORT_DIR/2-mozilla-removed.txt > $SUPPORT_DIR/5-mozilla-removed.txt
+iconv -f iso-8859-1 -t utf-8 $SUPPORT_DIR/5-mozilla-removed.txt > 5-mozilla-removed.txt
+comm -13 $SUPPORT_DIR/3-upstream.txt $SUPPORT_DIR/2-mozilla-added.txt > $SUPPORT_DIR/5-mozilla-added.txt
+iconv -f iso-8859-1 -t utf-8 $SUPPORT_DIR/5-mozilla-added.txt > 5-mozilla-added.txt
+
+# Clean up some files
+rm hunspell-en_US-mozilla.zip
+rm nosug
diff --git a/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/mozilla-exclusions.txt b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/mozilla-exclusions.txt
new file mode 100644
index 000000000000..eca039ff53d5
--- /dev/null
+++ b/extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/mozilla-exclusions.txt
@@ -0,0 +1,2 @@
+nigga/SM
+niggaz
diff --git a/tools/lint/shellcheck.yml b/tools/lint/shellcheck.yml
index d0b390d4e87e..0100e3d5cc25 100644
--- a/tools/lint/shellcheck.yml
+++ b/tools/lint/shellcheck.yml
@@ -2,6 +2,7 @@
 shellcheck:
     description: Shell script linter
     include:
+        - extensions/spellcheck/locales/en-US/hunspell/dictionary-sources/
         - taskcluster/docker/
     exclude: []
     # 1090: https://github.com/koalaman/shellcheck/wiki/SC1090