--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -4706,40 +4706,28 @@ MultiprocessBlockPolicy() {
   }
 
   /**
    * Avoids enabling e10s for certain locales that require bidi selection,
    * which currently doesn't work well with e10s.
    */
   bool disabledForBidi = false;
 
-  nsAutoCString locale;
   nsCOMPtr<nsIXULChromeRegistry> registry =
    mozilla::services::GetXULChromeRegistryService();
   if (registry) {
-     registry->GetSelectedLocale(NS_LITERAL_CSTRING("global"), locale);
-  }
-
-  int32_t index = locale.FindChar('-');
-  if (index >= 0) {
-    locale.Truncate(index);
-  }
-
-  if (locale.EqualsLiteral("ar") ||
-      locale.EqualsLiteral("fa") ||
-      locale.EqualsLiteral("he") ||
-      locale.EqualsLiteral("ur")) {
-    disabledForBidi = true;
+     disabledForBidi = registry->IsLocaleRTL(NS_LITERAL_CSTRING("global"));
   }
 
   if (disabledForBidi) {
     gMultiprocessBlockPolicy = kE10sDisabledForBidi;
     return gMultiprocessBlockPolicy;
   }
 
+
 #if defined(XP_MACOSX)
   // If for any reason we suspect acceleration will be disabled, disable
   // e10s auto start on mac.
 
   // Check prefs
   bool accelDisabled = gfxPrefs::GetSingleton().LayersAccelerationDisabled() &&
                        !gfxPrefs::LayersAccelerationForceEnabled();