diff -up thunderbird-60.6.1/intl/locale/LocaleService.cpp.debug thunderbird-60.6.1/intl/locale/LocaleService.cpp
--- thunderbird-60.6.1/intl/locale/LocaleService.cpp.debug	2019-05-15 08:15:14.602872505 +0200
+++ thunderbird-60.6.1/intl/locale/LocaleService.cpp	2019-05-15 08:15:53.717635322 +0200
@@ -643,8 +643,6 @@ LocaleService::GetDefaultLocale(nsACStri
     // just use our hard-coded default below.
     GetGREFileContents("update.locale", &locale);
     locale.Trim(" \t\n\r");
-    // This should never be empty.
-    MOZ_ASSERT(!locale.IsEmpty());
     if (SanitizeForBCP47(locale, true)) {
       mDefaultLocale.Assign(locale);
     }