--- a/browser/components/preferences/fonts.js
+++ b/browser/components/preferences/fonts.js
@@ -85,32 +85,34 @@ var gFontsDialog = {
     return preference.value == 1;
   },
 
   writeUseDocumentFonts() {
     var useDocumentFonts = document.getElementById("useDocumentFonts");
     return useDocumentFonts.checked ? 1 : 0;
   },
 
-  onBeforeAccept() {
-    // It would be good if we could avoid touching languages the pref pages won't use, but
-    // unfortunately the language group APIs (deducing language groups from language codes)
-    // are C++ - only. So we just check all the things the user touched:
-    // Don't care about anything up to 24px, or if this value is the same as set previously:
-    let preferences = Preferences.getAll().filter(pref => {
-      return pref.id.includes("font.minimum-size") && pref.value > 24 && pref.value != pref.valueFromPreferences;
-    });
-    if (!preferences.length) {
-      return true;
+  async confirmMinSizeChange() {
+    let menulist = document.getElementById("minSize");
+    let preference = menulist.getAttribute("preference");
+    let defaultValue = Preferences.get(preference).valueFromPreferences;
+    let oldValue = Preferences.get(preference).value;
+    let newValue = menulist.value;
+
+    if (newValue <= 24 || newValue == defaultValue) {
+      return;
     }
 
-    let strings = document.getElementById("bundlePreferences");
-    let title = strings.getString("veryLargeMinimumFontTitle");
-    let confirmLabel = strings.getString("acceptVeryLargeMinimumFont");
-    let warningMessage = strings.getString("veryLargeMinimumFontWarning");
+    let [title, warningMessage, confirmLabel] = await document.l10n.formatValues([
+      ["fonts-very-large-warning-title"],
+      ["fonts-very-large-warning-message"],
+      ["fonts-very-large-warning-accept"],
+    ]);
     let {Services} = ChromeUtils.import("resource://gre/modules/Services.jsm", {});
     let flags = Services.prompt.BUTTON_POS_1 * Services.prompt.BUTTON_TITLE_CANCEL |
                 Services.prompt.BUTTON_POS_0 * Services.prompt.BUTTON_TITLE_IS_STRING |
                 Services.prompt.BUTTON_POS_1_DEFAULT;
     let buttonChosen = Services.prompt.confirmEx(window, title, warningMessage, flags, confirmLabel, null, "", "", {});
-    return buttonChosen == 0;
+    if (buttonChosen != 0) {
+      menulist.value = oldValue;
+    }
   },
 };

--- a/browser/components/preferences/fonts.xul
+++ b/browser/components/preferences/fonts.xul
@@ -11,32 +11,30 @@
 <dialog id="FontsDialog" type="child" class="prefwindow"
         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
         data-l10n-id="fonts-window"
         data-l10n-attrs="title"
         buttons="accept,cancel,help"
         persist="lastSelected screenX screenY"
         role="dialog"
         helpTopic="prefs-fonts-and-colors"
-        ondialoghelp="openPrefsHelp()"
-        onbeforeaccept="return gFontsDialog.onBeforeAccept();">
+        ondialoghelp="openPrefsHelp()">
 
   <link rel="localization" href="browser/preferences/fonts.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"/>
 
   <keyset>
     <key data-l10n-id="fonts-window-close" modifiers="accel" oncommand="Preferences.close(event)"/>
   </keyset>
 
   <vbox id="FontsDialogPane" class="prefpane largeDialogContainer">
 
-    <stringbundle id="bundlePreferences" src="chrome://browser/locale/preferences/preferences.properties"/>
     <script type="application/javascript" src="chrome://mozapps/content/preferences/fontbuilder.js"/>
     <script type="application/javascript" src="chrome://browser/content/preferences/fonts.js"/>
 
     <!-- Fonts for: [ Language ] -->
     <groupbox>
       <caption>
         <hbox align="center">
           <label data-l10n-id="fonts-langgroup-header" control="selectLangs"/>
@@ -209,17 +207,17 @@
       </grid>
       <separator class="thin"/>
       <hbox flex="1">
         <spacer flex="1"/>
         <hbox align="center" pack="end">
           <label data-l10n-id="fonts-minsize" control="minSize"/>
           <!-- Please don't remove the wrapping hbox/vbox/box for these elements. It's used to properly compute the search tooltip position. -->
           <hbox>
-            <menulist id="minSize">
+            <menulist id="minSize" oncommand="gFontsDialog.confirmMinSizeChange();">
               <menupopup>
                 <menuitem value="0" data-l10n-id="fonts-minsize-none"/>
                 <menuitem value="9" label="9"/>
                 <menuitem value="10" label="10"/>
                 <menuitem value="11" label="11"/>
                 <menuitem value="12" label="12"/>
                 <menuitem value="13" label="13"/>
                 <menuitem value="14" label="14"/>

--- a/browser/components/preferences/in-content/preferences.xul
+++ b/browser/components/preferences/in-content/preferences.xul
@@ -35,23 +35,24 @@
       xmlns:html="http://www.w3.org/1999/xhtml"
       disablefastfind="true"
       data-l10n-id="pref-page"
       data-l10n-attrs="title">
 
   <link rel="localization" href="branding/brand.ftl"/>
   <link rel="localization" href="browser/branding/sync-brand.ftl"/>
   <link rel="localization" href="browser/preferences/preferences.ftl"/>
+  <!-- Used by fontbuilder.js -->
+  <link rel="localization" href="browser/preferences/fonts.ftl"/>
 
   <!-- Links below are only used for search-l10n-ids into subdialogs -->
   <link rel="localization" href="browser/preferences/blocklists.ftl"/>
   <link rel="localization" href="browser/preferences/clearSiteData.ftl"/>
   <link rel="localization" href="browser/preferences/colors.ftl"/>
   <link rel="localization" href="browser/preferences/connection.ftl"/>
-  <link rel="localization" href="browser/preferences/fonts.ftl"/>
   <link rel="localization" href="browser/preferences/languages.ftl"/>
   <link rel="localization" href="browser/preferences/permissions.ftl"/>
   <link rel="localization" href="browser/preferences/selectBookmark.ftl"/>
   <link rel="localization" href="browser/preferences/siteDataSettings.ftl"/>
 
   <script type="text/javascript" src="chrome://global/content/l10n.js"></script>
 
   <html:link rel="shortcut icon"

--- a/browser/locales/en-US/browser/preferences/fonts.ftl
+++ b/browser/locales/en-US/browser/preferences/fonts.ftl
@@ -146,8 +146,19 @@ fonts-languages-fallback-name-korean =
 fonts-languages-fallback-name-thai =
     .label = Thai
 fonts-languages-fallback-name-turkish =
     .label = Turkish
 fonts-languages-fallback-name-vietnamese =
     .label = Vietnamese
 fonts-languages-fallback-name-other =
     .label = Other (incl. Western European)
+
+fonts-very-large-warning-title = Large minimum font size
+fonts-very-large-warning-message = You have selected a very large minimum font size (more than 24 pixels). This may make it difficult or impossible to use some important configuration pages like this one.
+fonts-very-large-warning-accept = Keep my changes anyway
+
+# Variables:
+#   $name {string, "Arial"} - Name of the default font
+fonts-label-default =
+    .label = Default ({ $name })
+fonts-label-default-unnamed =
+    .label = Default

--- a/browser/locales/en-US/chrome/browser/preferences/preferences.properties
+++ b/browser/locales/en-US/chrome/browser/preferences/preferences.properties
@@ -4,25 +4,16 @@
 
 #### Security
 
 # LOCALIZATION NOTE: phishBefore uses %S to represent the name of the provider
 #                    whose privacy policy must be accepted (for enabling
 #                    check-every-page-as-I-load-it phishing protection).
 phishBeforeText=Selecting this option will send the address of web pages you are viewing to %S. To continue, please review and accept the following terms of service.
 
-#### Fonts
-
-labelDefaultFont=Default (%S)
-labelDefaultFontUnnamed=Default
-
-veryLargeMinimumFontTitle=Large minimum font size
-veryLargeMinimumFontWarning=You have selected a very large minimum font size (more than 24 pixels). This may make it difficult or impossible to use some important configuration pages like this one.
-acceptVeryLargeMinimumFont=Keep my changes anyway
-
 #### Master Password
 
 pw_change2empty_in_fips_mode=You are currently in FIPS mode. FIPS requires a non-empty Master Password.
 pw_change_failed_title=Password Change Failed
 
 #### Fonts
 
 # LOCALIZATION NOTE: The string represents a localized locale name

--- a/toolkit/mozapps/preferences/fontbuilder.js
+++ b/toolkit/mozapps/preferences/fontbuilder.js
@@ -36,22 +36,24 @@ var FontBuilder = {
 
     if (!this._allFonts)
       this._allFonts = await this.enumerator.EnumerateAllFontsAsync({});
 
     // Build the UI for the Default Font and Fonts for this CSS type.
     const popup = document.createElement("menupopup");
     let separator;
     if (fonts.length > 0) {
-      const bundlePreferences = document.getElementById("bundlePreferences");
-      let defaultLabel = defaultFont ?
-        bundlePreferences.getFormattedString("labelDefaultFont", [defaultFont]) :
-        bundlePreferences.getString("labelDefaultFontUnnamed");
       let menuitem = document.createElement("menuitem");
-      menuitem.setAttribute("label", defaultLabel);
+      if (defaultFont) {
+        document.l10n.setAttributes(menuitem, "fonts-label-default", {
+          name: defaultFont
+        });
+      } else {
+        document.l10n.setAttributes(menuitem, "fonts-label-default-unnamed");
+      }
       menuitem.setAttribute("value", ""); // Default Font has a blank value
       popup.appendChild(menuitem);
 
       separator = document.createElement("menuseparator");
       popup.appendChild(separator);
 
       for (let font of fonts) {
         menuitem = document.createElement("menuitem");