> AMO will continue to support listing and updating legacy add-ons after the release of 57 in order to have an easier transition. The exact cut-off time for thi

> AMO will continue to support listing and updating legacy add-ons after the release of 57 in order to have an easier transition. The exact cut-off time for this support hasn’t been determined yet. I'm not familiar with the release timelines, but I hope they keep that up at least until they stop supporting Firefox 52 ESR. I switched to it explicitly to keep my XUL add-ons working longer while the add-on makers/Mozilla catch up with the new API.