The simple-prefs module: https://addons.mozilla.org/en-US/developers/docs/sdk/latest/packages/addon-kit/simple-prefs.html has been in addon-kit for more than 6 months, marked as experimental. We should make it stable so we can remove the unsettling warnings and users can rely on it. If there's substantial work that needs to be done before we can declare the API stable, we should perhaps track that work using bugs that block this bug, then update the docs and metadata in this bug.