Mozilla Firefox is an open-source web browser, developed by the Mozilla Foundation. It uses Gecko as the rendering engine for its desktop versions and WebKit for iOS. Firefox has some features like tabbed browsing, spell checking, smart bookmarks, download manager, private browsing, and a screenshot tool. The tools provided also include web development tools, location-aware browsing, and an integrated search system. Firefox supports add-ons coded in HTML, CSS, JavaScript, and the WebExtensions API. It also provides productivity, privacy, and personalization features such as URL autosuggest, reader mode, third-party cookie blocking, a built-in password manager, and customization options. It works seamlessly with Google products and offers a "Facebook Container" extension to prevent tracking by Facebook and Instagram. Users can sync their devices for cross-device access to tabs, history, and bookmarks. Other features include Enhanced Tracking Protection and a Picture-in-Picture mode.