This extension allows you to inject any javascript code into the web page you are visiting. It remembers your page specific script and syncs it across all your devices. For example, if you want to change the background color of https://duckduckgo.com/ with light blue, you can inject the script 'document.body.style.backgroundColor = "lightblue";' using this extension. After that every time you open this web site, the back ground will be light blue automatically.