Download
The extension is available for Chrome, Firefox, Safari, and Microsoft Edge browsers.
For other Chromium-based browsers, e.g. Brave, you can follow the instructions for the Chrome browser.
Chrome
It's by far the most popular chess extension for Chrome with over 40k active users.
Firefox
It's by far the most popular chess extension for Firefox with close to 2k active users.
Safari
It's the only Safari extension that can scan chess diagrams from websites.
Microsoft Edge
You can install the extension directly from the Chrome Web Store.
Detailed installation instructions on how to do it: Add an extension to Microsoft Edge from the Chrome Web Store - look for a section called "Add an extension to Microsoft Edge from the Chrome Web Store" there.