You cannot update a WebExtensions add-on with a legacy add-on. Your users would not be able to use your new version because Firefox does not support this type of update.
Njamóžośo dodank typa WebExtensions pśez dodank starego typa aktualizěrowaś. Waše wužywarje njemógli wašu nowu wersiju wužywaś, dokulaž Firefox njepódpěra toś ten typ aktualizacije.