That’ll be HTML and javascript
You’ll need to (likely) implement implicit auth
In order to get an Access Token to call the API with. Example
https://barrycarlyon.github.io/twitch_misc/authentication/implicit_auth/
or
https://barrycarlyon.github.io/twitch_misc/examples/browse_following/
Alternatively your browser extension would phone your server for stream status instead, then you don’t have to prompt the browser extension users to login to Twitch