[DEPRECATED]
The X-XSS-Protection security header was created to control the built-in protection against Reflected Cross-Site Scripting (XSS) attacks in web browsers. In the past XSS protection was built into Internet Explorer, Chrome, Edge, and Safari. Firefox never implemented XSS protection. When a browser with built-in and activated XSS protections detected an XSS attack, the browser would remove the unsafe scripts from the page.