Shows when you are on a dev-version of a page by putting a border around the favicon.
Looks at the URL of the page you're on to see if it's a dev environment and adds a border to the favicon so you can easily tell if you're on a dev environment or not.
You can change in the options what URL hostname constitutes a dev environment, by default we look for:
- localhost
- 127.0.0.1
- Sites ending with .test