If you’ve ever noticed a slight but still annoying delay between pressing a key on your keyboard and seeing a letter appear on-screen, then you’ve experienced the First Input Delay.
The first input delay is caused when most browsers block any JavaScript, CSS, images or other assets which are loaded while the user types into the input fields.
This prevents unintended actions like changing tabs while the user is still typing. By default most browsers will only load a few characters of text before it triggers the FID.