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.
Man yatikïr ta nak'ëx jun WebExtensions tz'aqat rik'in legacy tz'aqat. Man xketikïr xtikokisaj ri k'ak'a' ruwäch ri okisanela' ruma chi ri Firefox man nuya' ta q'ij chi ke re kiwäch k'exoj re'.