::before creates a pseudo-element that is the first child of the element matched. It is often used to add cosmetic content to an element by using the content property. This element is inline by default.
The ::first-lineCSSpseudo-element applies styles only to the first line of an element. The amount of the text on the first line depends of numerous factors, like the width of the element, width of the document, and the font size of the text. As all pseudo-elements, ::first-line does not match any real HTML element.
The ::-moz-placeholderpseudo-element represents any form element displaying placeholder text. This allows web developers and theme designers to customize the appearance of placeholder text, which is a light grey color by default. This may not work well if you've changed the background color of your form fields to be a similar color, for example, so you can use this pseudo-element to change the placeholder text color.