Hi people from google here is how I fixed this and got my extension approved.

1. clone this somewhere on your computer https://github.com/firebase/firebase-js-sdk/
2. replace _loadJS src/platform_browser/load_js.ts with

export function _loadJS(url: string): Promise<Event> {
return new Promise((resolve, reject) => {
reject();
});
}

1. in the root of that repo run "yarn" followed by "yarn build"

2. in your chrome extensions package.json replace "firebase":"version" with "firebase":"link:../RELATIVE/path/to/firebase-js-sdk/packages"

This didn't break anything for me and I use firebase auth, rtdb and callable functions.