Not allowed in: Content scripts, Devtools pages

_ExperimentAPIChild
_ExperimentAPIParent
ExperimentAPI
APIChildScope
APIEvent
APIEvents
APIParentScope
APIPath
APIPaths
ExperimentURL
APIChildScope: "addon_child" | "content_child" | "devtools_child"
APIEvent: "startup"
APIEvents: APIEvent[]
APIParentScope: "addon_parent" | "content_parent" | "devtools_parent"
APIPath: string[]
APIPaths: APIPath[]
ExperimentURL: string