It's a Chrome extension that hides the Chromecast button, so you won't panic about accidentally clicking it. It should work with popular sites (YouTube, Twitch, etc.).
- Download the archive
- Go to
chrome://extensions/ - Turn on the developer mode
- Drag and drop downloaded archive on the page
It creates a style tag that adds the property display: none to necessary selectors.
Note that different sites have different selectors for the button, so the extension wouldn't work on some of them.