Web browsers act as an interface between users and web servers by allowing users to locate and display web pages. Major web browsers allow opening multiple pages simultaneously, refreshing pages, adding bookmarks, and blocking pop-ups. Browsers have a user interface and rendering engine. The history of web browsers began in the late 1980s and early browsers included WorldWideWeb, Mosaic, Netscape Navigator, and Internet Explorer. Popular modern browsers are Firefox, Safari, Chrome, Opera, and mobile-optimized browsers.