--- a/browser/components/preferences/applicationManager.js
+++ b/browser/components/preferences/applicationManager.js
@@ -7,29 +7,29 @@
 var gAppManagerDialog = {
   _removed: [],
 
   init: function appManager_init() {
     this.handlerInfo = window.arguments[0];
     Services.scriptloader.loadSubScript("chrome://browser/content/preferences/in-content/main.js",
       window);
     var pane = gMainPane;
-    var bundle = document.getElementById("appManagerBundle");
-    var contentText;
-    if (this.handlerInfo.type == TYPE_MAYBE_FEED)
-      contentText = bundle.getString("handleWebFeeds");
-    else {
-      var description = pane._describeType(this.handlerInfo);
-      var key =
-        (this.handlerInfo.wrappedHandlerInfo instanceof Ci.nsIMIMEInfo) ? "handleFile"
-                                                                        : "handleProtocol";
-        contentText = bundle.getFormattedString(key, [description]);
+
+    const appDescElem = document.getElementById("appDescription");
+    if (this.handlerInfo.type == TYPE_MAYBE_FEED) {
+      document.l10n.setAttributes(appDescElem, "app-manager-handle-webfeeds");
+    } else if (this.handlerInfo.wrappedHandlerInfo instanceof Ci.nsIMIMEInfo) {
+      document.l10n.setAttributes(appDescElem, "app-manager-handle-file", {
+        type: pane._describeType(this.handlerInfo)
+      });
+    } else {
+      document.l10n.setAttributes(appDescElem, "app-manager-handle-protocol", {
+        type: pane._describeType(this.handlerInfo)
+      });
     }
-    contentText = bundle.getFormattedString("descriptionApplications", [contentText]);
-    document.getElementById("appDescription").textContent = contentText;
 
     var list = document.getElementById("appList");
     var apps = this.handlerInfo.possibleApplicationHandlers.enumerate();
     while (apps.hasMoreElements()) {
       let app = apps.getNext();
       if (!pane.isValidHandlerApp(app))
         continue;
 
@@ -87,14 +87,14 @@ var gAppManagerDialog = {
     var address = "";
     if (app instanceof Ci.nsILocalHandlerApp)
       address = app.executable.path;
     else if (app instanceof Ci.nsIWebHandlerApp)
       address = app.uriTemplate;
     else if (app instanceof Ci.nsIWebContentHandlerInfo)
       address = app.uri;
     document.getElementById("appLocation").value = address;
-    var bundle = document.getElementById("appManagerBundle");
-    var appType = app instanceof Ci.nsILocalHandlerApp ? "descriptionLocalApp"
-                                                       : "descriptionWebApp";
-    document.getElementById("appType").value = bundle.getString(appType);
+    const l10nId = app instanceof Ci.nsILocalHandlerApp ? "app-manager-local-app-info"
+                                                        : "app-manager-web-app-info";
+    const appTypeElem = document.getElementById("appType");
+    document.l10n.setAttributes(appTypeElem, l10nId);
   }
 };

--- a/browser/components/preferences/applicationManager.xul
+++ b/browser/components/preferences/applicationManager.xul
@@ -1,27 +1,28 @@
 <?xml version="1.0"?>
 <!-- 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/. -->
 
 <?xml-stylesheet href="chrome://global/skin/"?>
 
-<!DOCTYPE dialog SYSTEM "chrome://browser/locale/preferences/applicationManager.dtd">
-
 <dialog id="appManager"
         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
         buttons="accept,cancel"
         onload="gAppManagerDialog.init();"
         ondialogaccept="gAppManagerDialog.onOK();"
         ondialogcancel="gAppManagerDialog.onCancel();"
-        title="&appManager.title;"
-        style="&appManager.style;"
+        data-l10n-id="app-manager-window"
+        data-l10n-attrs="title, style"
         persist="screenX screenY">
 
+  <link rel="localization" href="browser/preferences/applicationManager.ftl"/>
+  <script type="application/javascript" src="chrome://global/content/l10n.js"></script>
+
   <script type="application/javascript"
           src="chrome://browser/content/utilityOverlay.js"/>
   <script type="application/javascript"
           src="chrome://global/content/preferencesBindings.js"/>
   <script type="application/javascript"
           src="chrome://browser/content/preferences/applicationManager.js"/>
 
   <commandset id="appManagerCommandSet">
@@ -29,31 +30,27 @@
              oncommand="gAppManagerDialog.remove();"
              disabled="true"/>
   </commandset>
 
   <keyset id="appManagerKeyset">
     <key id="delete" keycode="VK_DELETE" command="cmd_remove"/>
   </keyset>
 
-  <stringbundleset id="appManagerBundleset">
-    <stringbundle id="appManagerBundle"
-                  src="chrome://browser/locale/preferences/applicationManager.properties"/>
-  </stringbundleset>
-
-  <description id="appDescription"/>
+  <!-- The &#160; character is required here to calculate the dialog height -->
+  <description id="appDescription">&#160;</description>
   <separator class="thin"/>
   <hbox flex="1">
     <listbox id="appList" onselect="gAppManagerDialog.onSelect();" flex="1"/>
     <vbox>
       <button id="remove"
-              label="&remove.label;"
-              accesskey="&remove.accesskey;"
+              data-l10n-id="app-manager-remove"
               command="cmd_remove"/>
       <spacer flex="1"/>
     </vbox>
   </hbox>
   <vbox id="appDetails">
     <separator class="thin"/>
-    <label id="appType"/>
+    <!-- The &#160; character is required here to calculate the dialog height -->
+    <label id="appType">&#160;</label>
     <textbox id="appLocation" readonly="true" class="plain"/>
   </vbox>
 </dialog>

--- a/browser/components/preferences/in-content/preferences.xul
+++ b/browser/components/preferences/in-content/preferences.xul
@@ -97,21 +97,16 @@
                 src="chrome://branding/locale/brand.properties"/>
   <stringbundle id="bundlePreferences"
                 src="chrome://browser/locale/preferences/preferences.properties"/>
   <stringbundle id="pkiBundle"
                 src="chrome://pippki/locale/pippki.properties"/>
   <stringbundle id="browserBundle"
                 src="chrome://browser/locale/browser.properties"/>
 
-  <stringbundleset id="appManagerBundleset">
-    <stringbundle id="appManagerBundle"
-                  src="chrome://browser/locale/preferences/applicationManager.properties"/>
-  </stringbundleset>
-
   <stack flex="1">
   <hbox flex="1">
 
     <vbox class="navigation">
       <!-- category list -->
       <richlistbox id="categories">
         <richlistitem id="category-general"
                       class="category"

new file mode 100644
--- /dev/null
+++ b/browser/locales/en-US/browser/preferences/applicationManager.ftl
@@ -0,0 +1,27 @@
+# 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/.
+
+app-manager-window =
+    .title = Application details
+    .style = width: 30em; min-height: 20em;
+
+app-manager-remove =
+    .label = Remove
+    .accesskey = R
+
+app-manager-handle-webfeeds = The following applications can be used to handle Web Feeds.
+
+# Variables:
+#   $type (String) - the URI scheme of the link (e.g. mailto:)
+app-manager-handle-protocol = The following applications can be used to handle { $type } links.
+
+# Variables:
+#   $type (String) - the MIME type (e.g. application/binary)
+app-manager-handle-file = The following applications can be used to handle { $type } content.
+
+## These strings are followed, on a new line,
+## by the URL or path of the application.
+
+app-manager-web-app-info = This web application is hosted at:
+app-manager-local-app-info = This application is located at:

deleted file mode 100644
--- a/browser/locales/en-US/chrome/browser/preferences/applicationManager.dtd
+++ /dev/null
@@ -1,8 +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 appManager.title     "Application details">
-<!ENTITY appManager.style     "width: 30em; min-height: 20em;">
-<!ENTITY remove.label         "Remove">
-<!ENTITY remove.accesskey     "R">

deleted file mode 100644
--- a/browser/locales/en-US/chrome/browser/preferences/applicationManager.properties
+++ /dev/null
@@ -1,14 +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/.
-
-# LOCALIZATION NOTE
-# in descriptionApplications, %S will be replaced by one of the 3 following strings
-descriptionApplications=The following applications can be used to handle %S.
-
-handleProtocol=%S links
-handleWebFeeds=Web Feeds
-handleFile=%S content
-
-descriptionWebApp=This web application is hosted at:
-descriptionLocalApp=This application is located at:

--- a/browser/locales/jar.mn
+++ b/browser/locales/jar.mn
@@ -50,18 +50,16 @@
     locale/browser/places/bookmarkProperties.properties (%chrome/browser/places/bookmarkProperties.properties)
     locale/browser/safebrowsing/phishing-afterload-warning-message.dtd (%chrome/browser/safebrowsing/phishing-afterload-warning-message.dtd)
     locale/browser/safebrowsing/report-phishing.dtd                    (%chrome/browser/safebrowsing/report-phishing.dtd)
     locale/browser/safebrowsing/safebrowsing.properties   (%chrome/browser/safebrowsing/safebrowsing.properties)
     locale/browser/feeds/subscribe.dtd              (%chrome/browser/feeds/subscribe.dtd)
     locale/browser/feeds/subscribe.properties       (%chrome/browser/feeds/subscribe.properties)
     locale/browser/migration/migration.dtd         (%chrome/browser/migration/migration.dtd)
     locale/browser/migration/migration.properties  (%chrome/browser/migration/migration.properties)
-    locale/browser/preferences/applicationManager.dtd     (%chrome/browser/preferences/applicationManager.dtd)
-    locale/browser/preferences/applicationManager.properties     (%chrome/browser/preferences/applicationManager.properties)
     locale/browser/preferences/blocklists.dtd         (%chrome/browser/preferences/blocklists.dtd)
     locale/browser/preferences/clearSiteData.dtd      (%chrome/browser/preferences/clearSiteData.dtd)
     locale/browser/preferences/clearSiteData.properties     (%chrome/browser/preferences/clearSiteData.properties)
     locale/browser/preferences/colors.dtd             (%chrome/browser/preferences/colors.dtd)
     locale/browser/preferences/connection.dtd         (%chrome/browser/preferences/connection.dtd)
     locale/browser/preferences/content.dtd            (%chrome/browser/preferences/content.dtd)
     locale/browser/preferences/fonts.dtd              (%chrome/browser/preferences/fonts.dtd)
     locale/browser/preferences/languages.dtd          (%chrome/browser/preferences/languages.dtd)

new file mode 100644
--- /dev/null
+++ b/python/l10n/fluent_migrations/bug_1451992_preferences_applicationManager.py
@@ -0,0 +1,116 @@
+# 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 EXTERNAL_ARGUMENT
+from fluent.migrate import COPY, REPLACE
+
+def migrate(ctx):
+    """Bug 1451992 - Migrate Preferences::Subdialogs::ApplicationManager to Fluent, part {index}."""
+
+    ctx.add_transforms(
+        'browser/browser/preferences/applicationManager.ftl',
+        'browser/browser/preferences/applicationManager.ftl',
+        [
+            FTL.Message(
+                id=FTL.Identifier('app-manager-window'),
+                attributes=[
+                    FTL.Attribute(
+                        FTL.Identifier('title'),
+                        COPY(
+                            'browser/chrome/browser/preferences/applicationManager.dtd',
+                            'appManager.title',
+                        ),
+                    ),
+                    FTL.Attribute(
+                        FTL.Identifier('style'),
+                        COPY(
+                            'browser/chrome/browser/preferences/applicationManager.dtd',
+                            'appManager.style',
+                        ),
+                    ),
+                ],
+            ),
+            FTL.Message(
+                id=FTL.Identifier('app-manager-remove'),
+                attributes=[
+                    FTL.Attribute(
+                        FTL.Identifier('label'),
+                        COPY(
+                            'browser/chrome/browser/preferences/applicationManager.dtd',
+                            'remove.label',
+                        ),
+                    ),
+                    FTL.Attribute(
+                        FTL.Identifier('accesskey'),
+                        COPY(
+                            'browser/chrome/browser/preferences/applicationManager.dtd',
+                            'remove.accesskey',
+                        ),
+                    ),
+                ],
+            ),
+            FTL.Message(
+                id=FTL.Identifier('app-manager-handle-webfeeds'),
+                value=REPLACE(
+                    'browser/chrome/browser/preferences/applicationManager.properties',
+                    'descriptionApplications',
+                    {
+                        '%S': COPY(
+                            'browser/chrome/browser/preferences/applicationManager.properties',
+                            'handleWebFeeds',
+                        )
+                    }
+                ),
+            ),
+            FTL.Message(
+                id=FTL.Identifier('app-manager-handle-protocol'),
+                value=REPLACE(
+                    'browser/chrome/browser/preferences/applicationManager.properties',
+                    'descriptionApplications',
+                    {
+                        '%S': REPLACE(
+                            'browser/chrome/browser/preferences/applicationManager.properties',
+                            'handleProtocol',
+                            {
+                                '%S': EXTERNAL_ARGUMENT('type')
+                            }
+                        )
+                    }
+                ),
+            ),
+            FTL.Message(
+                id=FTL.Identifier('app-manager-handle-file'),
+                value=REPLACE(
+                    'browser/chrome/browser/preferences/applicationManager.properties',
+                    'descriptionApplications',
+                    {
+                        '%S': REPLACE(
+                            'browser/chrome/browser/preferences/applicationManager.properties',
+                            'handleFile',
+                            {
+                                '%S': EXTERNAL_ARGUMENT('type')
+                            }
+                        )
+                    }
+                ),
+            ),
+            FTL.Message(
+                id=FTL.Identifier('app-manager-web-app-info'),
+                value=COPY(
+                    'browser/chrome/browser/preferences/applicationManager.properties',
+                    'descriptionWebApp',
+                ),
+            ),
+            FTL.Message(
+                id=FTL.Identifier('app-manager-local-app-info'),
+                value=COPY(
+                    'browser/chrome/browser/preferences/applicationManager.properties',
+                    'descriptionLocalApp',
+                ),
+            ),
+        ]
+    )