Use DOMContentLoaded event: This ensures that all the HTML elements are loaded before executing your JavaScript logic. This event will run after the HTML content is fully loaded, but before the page's external resources like images, stylesheets, etc., are loaded.

Use input event on form fields: The input event fires when an input field is updated, including when Firefox autofills a value. This will help you determine whether the form was populated by cached data.

Check the value of inputs: In the input event handler, compare the field's value to a stored default or an empty state to determine if it has been autofilled.