diff -up firefox-63.0.1/intl/locale/LocaleService.cpp.old firefox-63.0.1/intl/locale/LocaleService.cpp
--- firefox-63.0.1/intl/locale/LocaleService.cpp.old 2018-11-14 13:34:16.338285161 +0100
+++ firefox-63.0.1/intl/locale/LocaleService.cpp 2018-11-14 13:34:21.438270308 +0100
@@ -708,7 +708,6 @@ LocaleService::GetDefaultLocale(nsACStri
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);
}