diff --git a/browser/components/nsBrowserGlue.js b/browser/components/nsBrowserGlue.js
index 41ec5c9d1d5..5b4d902af56 100644
--- a/browser/components/nsBrowserGlue.js
+++ b/browser/components/nsBrowserGlue.js
@@ -1661,7 +1661,7 @@ BrowserGlue.prototype = {
   },
 
   _migrateUI: function BG__migrateUI() {
-    const UI_VERSION = 28;
+    const UI_VERSION = 29;
     const BROWSER_DOCURL = "chrome://browser/content/browser.xul";
     let currentUIVersion = 0;
     try {
@@ -2016,6 +2016,21 @@ BrowserGlue.prototype = {
       Services.prefs.clearUserPref("browser.devedition.showCustomizeButton");
     }
 
+    if (currentUIVersion < 29) {
+      let group = null;
+      try {
+        group = Services.prefs.getComplexValue("font.language.group",
+                                               Ci.nsIPrefLocalizedString);
+      } catch (ex) {}
+      if (group &&
+          ["tr", "x-baltic", "x-central-euro"].some(g => g == group.data)) {
+        // Latin groups were consolidated.
+        group.data = "x-western";
+        Services.prefs.setComplexValue("font.language.group",
+                                       Ci.nsIPrefLocalizedString, group);
+      }
+    }
+
     // Update the migration version.
     Services.prefs.setIntPref("browser.migration.version", UI_VERSION);
   },