拡張作者に2月末に来たメールのUpcoming Changesは
ESR 52 is the last release that will support legacy extensions. When ESR 52 is discontinued on August 21, 2018, legacy extensions will be removed from addons.mozilla.org.
サポ終わったら消しますだったのが

5月末のメールは
ESR 52 has reached end of life and will stop being supported on September 5, 2018. This is the last release that supports legacy extensions.
と言及してないのでぶれてるのかな？