In the manifest it has a special "experiment_apis": "experiment_apis": { "skeleton": { "schema": "experiments/skeleton/schema.json",

In the manifest it has a special "experiment_apis": "experiment_apis": { "skeleton": { "schema": "experiments/skeleton/schema.json", "parent": { "scopes": [ "addon_parent" ], "script": "experiments/skeleton/api.js", "paths": [ [ "experiments", "skeleton" ] ] } } } Only Mozilla can use these on release versions of Firefox. If you want some more details then try here: https://firefox-source-docs.mozilla.org/toolkit/components/extensions/webextensions/index.html https://firefox-source-docs.mozilla.org/toolkit/components/e...