Firefox

Firefox is Mozilla's open-source browser and the main remaining alternative to the Chromium engine, which matters for the web as a whole — a single rendering engine across all browsers would make one company's decisions the de facto standard.

It has strong privacy defaults, including blocking of cross-site trackers, and container tabs that isolate sites from each other's cookies — genuinely useful for keeping multiple accounts separate.

Its extension ecosystem is smaller than Chrome's but covers the widely used categories, and its developer tools are capable if less commonly used.