ruffle/web/packages/extension/js/index.js

import { PublicAPI, SourceAPI } from "ruffle-core";

window.RufflePlayer = PublicAPI.negotiate(
    window.RufflePlayer,
    "extension",
    new SourceAPI("extension")
);

if (obfuscated_event_prefix) {
    document.addEventListener(
        obfuscated_event_prefix + "_request",
        function (e) {
            let body = JSON.parse(e.detail);
            let response = {};

            if (body.action === "get_page_options") {
                //response.page_options = page_options;
            }

            let event = new CustomEvent(obfuscated_event_prefix + "_response", {
                detail: JSON.stringify(response),
            });
            document.dispatchEvent(event);
        }
    );
}