This is a Manifest v3 Chrome Extension with the ability to send highlights from a Scribd/Everand book to your Readwise account. Simply open the book, click the extension icon, and click the "Export to Readwise" button. In contrast, here's the way Readwise asks you to import from Scribd.
This extension contains both a manifest.json and a manifest.firefox.json. If you need to build this extension for Firefox, you must rename the original manifest.json file to manifest.chrome.json and rename the manifest.firefox.json file to manifest.json.