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);
}