diff --git a/browser/base/jar.mn b/browser/base/jar.mn
index ef8d5542bc06..6f6cd4629420 100644
--- a/browser/base/jar.mn
+++ b/browser/base/jar.mn
@@ -130,5 +130,4 @@ browser.jar:
 # L10n resources and overrides.
 % override chrome://global/locale/appstrings.properties chrome://browser/locale/appstrings.properties
 % override chrome://global/locale/netError.dtd chrome://browser/locale/netError.dtd
-% override chrome://mozapps/locale/downloads/settingsChange.dtd chrome://browser/locale/downloads/settingsChange.dtd
 % override chrome://global/locale/app-extension-fields.properties chrome://browser/locale/app-extension-fields.properties
diff --git a/browser/locales/en-US/chrome/overrides/settingsChange.dtd b/browser/locales/en-US/chrome/overrides/settingsChange.dtd
deleted file mode 100644
index 1357b92fad2c..000000000000
--- a/browser/locales/en-US/chrome/overrides/settingsChange.dtd
+++ /dev/null
@@ -1,7 +0,0 @@
-<!-- -*- Mode: Java; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- -->
-<!-- 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/. -->
-
-<!ENTITY  settingsChangePreferences.label  "Settings can be changed using the Applications tab in &brandShortName;'s Preferences.">
-<!ENTITY  settingsChangeOptions.label      "Settings can be changed using the Applications tab in &brandShortName;'s Options.">
diff --git a/browser/locales/jar.mn b/browser/locales/jar.mn
index 2268e99c1b5e..62c281b9e68e 100644
--- a/browser/locales/jar.mn
+++ b/browser/locales/jar.mn
@@ -48,7 +48,6 @@
 # the following files are browser-specific overrides
     locale/browser/netError.dtd                (%chrome/overrides/netError.dtd)
     locale/browser/appstrings.properties       (%chrome/overrides/appstrings.properties)
-    locale/browser/downloads/settingsChange.dtd  (%chrome/overrides/settingsChange.dtd)
     locale/browser/newInstall.dtd                  (%chrome/browser/newInstall.dtd)
     locale/browser/brandings.dtd                   (%chrome/browser/brandings.dtd)
     locale/browser/fxmonitor.properties            (%chrome/browser/fxmonitor.properties)
diff --git a/python/l10n/fluent_migrations/bug_1668284_settings_change.py b/python/l10n/fluent_migrations/bug_1668284_settings_change.py
new file mode 100644
index 000000000000..0273c3f368f8
--- /dev/null
+++ b/python/l10n/fluent_migrations/bug_1668284_settings_change.py
@@ -0,0 +1,61 @@
+# coding=utf8
+
+# Any copyright is dedicated to the Public Domain.
+# http://creativecommons.org/publicdomain/zero/1.0/
+
+from __future__ import absolute_import
+import fluent.syntax.ast as FTL
+from fluent.migrate.helpers import transforms_from
+from fluent.migrate import REPLACE, COPY
+from fluent.migrate.helpers import MESSAGE_REFERENCE, TERM_REFERENCE
+
+def migrate(ctx):
+    """Bug 1668284 - Unknown content type change settings label is no longer accurate, part {index}."""
+
+    ctx.add_transforms(
+        "toolkit/toolkit/global/unknownContentType.ftl",
+        "toolkit/toolkit/global/unknownContentType.ftl",
+        [
+            FTL.Message(
+                id=FTL.Identifier("unknowncontenttype-settingschange"),
+                attributes=[
+                    FTL.Attribute(
+                        id=FTL.Identifier("value"),
+                        value=FTL.Pattern(
+                            elements=[
+                                FTL.Placeable(
+                                    expression=FTL.SelectExpression(
+                                        selector=MESSAGE_REFERENCE("PLATFORM()"),
+                                        variants=[
+                                            FTL.Variant(
+                                                key=FTL.Identifier("windows"),
+                                                default=False,
+                                                value=REPLACE(
+                                                    "toolkit/chrome/mozapps/downloads/settingsChange.dtd",
+                                                    "settingsChangeOptions.label",
+                                                    {
+                                                        "&brandShortName;": TERM_REFERENCE("brand-short-name"),
+                                                    },
+                                                )
+                                            ),
+                                            FTL.Variant(
+                                                key=FTL.Identifier("other"),
+                                                default=True,
+                                                value=REPLACE(
+                                                    "toolkit/chrome/mozapps/downloads/settingsChange.dtd",
+                                                    "settingsChangePreferences.label",
+                                                    {
+                                                        "&brandShortName;": TERM_REFERENCE("brand-short-name"),
+                                                    },
+                                                )
+                                            )
+                                        ]
+                                    )
+                                )
+                            ]
+                        )
+                    )
+                ]
+            )
+        ]
+    )
diff --git a/toolkit/locales/en-US/chrome/mozapps/downloads/settingsChange.dtd b/toolkit/locales/en-US/chrome/mozapps/downloads/settingsChange.dtd
deleted file mode 100644
index f28f7f341828..000000000000
--- a/toolkit/locales/en-US/chrome/mozapps/downloads/settingsChange.dtd
+++ /dev/null
@@ -1,6 +0,0 @@
-<!-- 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/. -->
-
-<!ENTITY  settingsChangePreferences.label  "Settings can be changed in &brandShortName;'s Preferences.">
-<!ENTITY  settingsChangeOptions.label      "Settings can be changed in &brandShortName;'s Options.">
diff --git a/toolkit/locales/en-US/toolkit/global/unknownContentType.ftl b/toolkit/locales/en-US/toolkit/global/unknownContentType.ftl
index d6373459f3bb..c4b09829b3c4 100644
--- a/toolkit/locales/en-US/toolkit/global/unknownContentType.ftl
+++ b/toolkit/locales/en-US/toolkit/global/unknownContentType.ftl
@@ -5,3 +5,10 @@
 unknowncontenttype-handleinternally =
     .label = Open with { -brand-short-name }
     .accesskey = e
+
+unknowncontenttype-settingschange =
+    .value =
+        { PLATFORM() ->
+            [windows] Settings can be changed in { -brand-short-name }'s Options.
+           *[other] Settings can be changed in { -brand-short-name }'s Preferences.
+        }
diff --git a/toolkit/locales/jar.mn b/toolkit/locales/jar.mn
index e1ec42567b77..e0136f5833b9 100644
--- a/toolkit/locales/jar.mn
+++ b/toolkit/locales/jar.mn
@@ -66,7 +66,6 @@
 % locale mozapps @AB_CD@ %locale/@AB_CD@/mozapps/
   locale/@AB_CD@/mozapps/downloads/unknownContentType.properties  (%chrome/mozapps/downloads/unknownContentType.properties)
   locale/@AB_CD@/mozapps/downloads/unknownContentType.dtd         (%chrome/mozapps/downloads/unknownContentType.dtd)
-  locale/@AB_CD@/mozapps/downloads/settingsChange.dtd             (%chrome/mozapps/downloads/settingsChange.dtd)
   locale/@AB_CD@/mozapps/downloads/downloads.properties           (%chrome/mozapps/downloads/downloads.properties)
   locale/@AB_CD@/mozapps/extensions/extensions.dtd                (%chrome/mozapps/extensions/extensions.dtd)
 #ifndef MOZ_FENNEC
diff --git a/toolkit/mozapps/downloads/content/unknownContentType.xhtml b/toolkit/mozapps/downloads/content/unknownContentType.xhtml
index 9a9551d59a43..23dbf623304c 100644
--- a/toolkit/mozapps/downloads/content/unknownContentType.xhtml
+++ b/toolkit/mozapps/downloads/content/unknownContentType.xhtml
@@ -12,8 +12,6 @@
   %brandDTD;
   <!ENTITY % uctDTD SYSTEM "chrome://mozapps/locale/downloads/unknownContentType.dtd" >
   %uctDTD;
-  <!ENTITY % scDTD SYSTEM "chrome://mozapps/locale/downloads/settingsChange.dtd" >
-  %scDTD;
 ]>
 
 <window id="unknownContentTypeWindow"
@@ -104,11 +102,9 @@
       </hbox>
 
       <separator/>
-#ifdef XP_UNIX
-      <description id="settingsChange" hidden="true">&settingsChangePreferences.label;</description>
-#else
-      <description id="settingsChange" hidden="true">&settingsChangeOptions.label;</description>
-#endif
+
+      <description id="settingsChange" hidden="true" data-l10n-id="unknowncontenttype-settingschange"/>
+
       <separator class="thin"/>
     </vbox>
   </vbox>