https://developer.mozilla.org/en-US/Add-ons/WebExtensions/manifest.json does not mention that it supports comments in the JSON. (same as with translations in _locales
etc.)
However, you do mention in
https://blog.mozilla.org/addons/2016/07/14/webextensions-support-on-amo/
…that you support comments in the JSON files, because Chromes does.
So should not this be documented, if it is now “officially” supported?