The FID of a site is important to maintain. To do this, make sure that the website is optimized and has Google's New Ranking Signals in 2021. It can be done by reducing long tasks scripts; removing unused javascript files from DOM cache for faster loading time; minifying JavaScript code before executing it at runtime so its size will not increase as more codes are being executed or when caches refresh compressing requested assets found on server with Gzip compression which reduces HTTP requests made to web servers thus increasing speed while using less bandwidth.