Firefox is a free, open-source web browser developed by Mozilla, a non-profit foundation. It is the main browser not built on Chromium, running instead on Mozilla's own Gecko engine — which is the reason it matters beyond its feature list, since an independent engine is what keeps web standards from being defined by a single implementation.
Privacy is where Firefox differentiates itself. Enhanced Tracking Protection blocks cross-site trackers, social media trackers, cryptominers and fingerprinting scripts by default, without configuration. Total Cookie Protection isolates cookies to the site that set them, so a tracker embedded on many sites cannot follow you between them. Container tabs go further, letting you keep separate logged-in identities — work and personal, or two accounts on one service — isolated in the same window.
The extension ecosystem is large and includes content blockers that operate with fewer restrictions than equivalents on some Chromium browsers. A Firefox Account syncs bookmarks, history, passwords and open tabs across devices, end-to-end encrypted.
Other features include a built-in reader mode, PDF viewer, screenshot tool, picture-in-picture video, and a set of developer tools that are among the better ones available.
Firefox runs on Windows, macOS, Linux, Android and iOS, and is free with no paid tier for the browser itself.
