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/e...

Also how can I verify that intermediate certificate? Is that a base64 encoded string?

Where does it say specifically on that page you linked that only Mozilla can use these apis?

It's installed as a study addon, only Mozilla could install these.

> It's installed as a study addon, only Mozilla could install these.

And that gives it access to use `Cc`/Components.classes?

Not familiar with the specifics, just know that Mozilla uses this mechanism to sometimes ship experimental features to a select group of Firefox users that have it enabled and they used it today to issue this hotfix to anyone who has field studies enabled.