The Starlit browser extension reads the Twitch user IDs and usernames of chatters visible on the Twitch page you are viewing and sends them to starlit.gg to look up their public Starlit cosmetics. When you sign in, the extension stores a device token in your browser's extension storage and sends it to starlit.gg to load your own profile and settings; you can revoke it from your Starlit account. The extension does not read, store or transmit chat message text, browsing history or any other page content, and it contains no advertising or analytics.

Full policy: https://starlit.gg/privacy