diff --git a/mobile/android/base/java/org/mozilla/gecko/BrowserLocaleManager.java b/mobile/android/base/java/org/mozilla/gecko/BrowserLocaleManager.java
index ba1f328483b3..1d24251d277c 100644
--- a/mobile/android/base/java/org/mozilla/gecko/BrowserLocaleManager.java
+++ b/mobile/android/base/java/org/mozilla/gecko/BrowserLocaleManager.java
@@ -106,6 +106,10 @@ public class BrowserLocaleManager implements LocaleManager {
                 systemLocaleDidChange = true;
 
                 Log.d(LOG_TAG, "System locale changed from " + current + " to " + systemLocale);
+
+                // If the OS locale changed, we need to tell Gecko.
+                final SharedPreferences prefs = GeckoSharedPrefs.forProfile(context);
+                BrowserLocaleManager.storeAndNotifyOSLocale(prefs, systemLocale);
             }
         };
         context.registerReceiver(receiver, new IntentFilter(Intent.ACTION_LOCALE_CHANGED));
@@ -208,6 +212,7 @@ public class BrowserLocaleManager implements LocaleManager {
         final String osLocaleString = osLocale.toString();
 
         if (osLocaleString.equals(lastOSLocale)) {
+            Log.d(LOG_TAG, "Previous locale " + lastOSLocale + " same as new. Doing nothing.");
             return;
         }
 
@@ -218,6 +223,7 @@ public class BrowserLocaleManager implements LocaleManager {
         // a Java locale string.
         final GeckoBundle data = new GeckoBundle(1);
         data.putString("languageTag", Locales.getLanguageTag(osLocale));
+
         EventDispatcher.getInstance().dispatch("Locale:OS", data);
     }
 
@@ -304,6 +310,10 @@ public class BrowserLocaleManager implements LocaleManager {
     }
 
     private SharedPreferences getSharedPreferences(Context context) {
+        // We should be using per-profile prefs here, because we're tracking against
+        // a Gecko pref. The same applies to the locale switcher!
+        // Bug 940575, Bug 873166 are relevant, and see Bug 1378501 for the commit
+        // that added this comment.
         return GeckoSharedPrefs.forApp(context);
     }
 
diff --git a/mobile/android/chrome/content/browser.js b/mobile/android/chrome/content/browser.js
index d1d6906e2a07..c93df2141b5b 100644
--- a/mobile/android/chrome/content/browser.js
+++ b/mobile/android/chrome/content/browser.js
@@ -1742,6 +1742,9 @@ var BrowserApp = {
         let appLocale = this.getUALocalePref();
 
         this.computeAcceptLanguages(languageTag, appLocale);
+
+        // Rebuild strings, in case we're mirroring OS locale.
+        Strings.flush();
         break;
       }
 
@@ -1752,6 +1755,11 @@ var BrowserApp = {
           Services.locale.setRequestedLocales([]);
         }
 
+        console.log("Gecko display locale: " + this.getUALocalePref());
+
+        // Rebuild strings to reflect the new locale.
+        Strings.flush();
+
         // Make sure we use the right Accept-Language header.
         let osLocale;
         try {