Firefox is the open-source web browser developed by Mozilla Foundation since 2002. The only major browser not derived from Chromium (which powers Chrome, Edge, Brave, Opera, Vivaldi). Funded primarily by the Mozilla Corporation’s revenue from default-search-engine deals (around 80% of Mozilla revenue is from Google for the default search position). Around 3% of global browser market share in 2026, down from peak 30% in 2010.
What it means in practice
Firefox’s structural value is engine diversity. A web in which Chromium powers 90% of browsers means web standards effectively reflect Google’s implementation choices, with no independent counterweight. Firefox is that counterweight, plus it is the only major browser whose privacy posture is set by a nonprofit foundation rather than an ad-tech company (Google, Microsoft, Apple). The privacy out-of-the-box is decent (Enhanced Tracking Protection on by default, container support, Multi-Account Containers extension). The privacy ceiling is high with hardening: arkenfox/user.js is a community-maintained configuration that turns Firefox into a near-Tor-Browser-grade hardened build for daily use, at the cost of breaking sites that depend on tracking.
Where it shows up
Default browser on: most Linux distributions, Tails (with Tor Browser as the actual user-facing browser), some privacy-focused Android distributions. Recommended for: anyone who values engine diversity, anyone running container-based identity separation (Mozilla Containers), and developers who want an alternative to the Chromium developer-tools monopoly. Mozilla’s recent strategic missteps (sponsored content in the address bar, AI features added without opt-out, the 2024 Anonym ad-tech acquisition) have eroded some trust without changing the underlying argument that an independent engine matters. The realistic alternatives: Brave (Chromium with privacy patches, complicated by the BAT cryptocurrency), LibreWolf (a Firefox fork with arkenfox baked in), Mullvad Browser (Tor Project + Mullvad collaboration, Tor Browser without Tor).
What you can change today
Install Firefox or LibreWolf as your daily browser. In Firefox: Settings, Privacy and Security, set Enhanced Tracking Protection to Strict, enable Always Use Private Browsing Mode if your threat model justifies it, install uBlock Origin and Multi-Account Containers as extensions. For higher-tier hardening: apply the arkenfox user.js (github.com/arkenfox/user.js) which adjusts hundreds of about:config settings to a defensible baseline. For the strongest browser-level privacy: use Mullvad Browser (mullvad.net/download/browser) for non-Tor sessions, Tor Browser for Tor sessions; both come with arkenfox-equivalent hardening preconfigured.