The new version of Firefox is very sleek and very fast, while retaining backwards compatibility with older plugins. An easy upgrade for users of the previous version, a quick install for everyone else. An absolute must-have for any web developer. Among the new features are a new UI (Photon), a new CSS engine (Stylo), and some substantial improvements on the already excellent rendering engine.

Browsers continually vie with one another for speed, features, stability, standards compliance, and security so this may not be true for long but, right now, Firefox Quantum comfortably leads the pack on most of those fronts. I am very fond of Firefox for many reasons, not least being that it is the most open of mainstream browsers, and the only one supported by a not-for-profit foundation that exists solely to provide the best and most standards-compliant products, not to please its shareholders (well - its tight integration and buddying up with Pocket bothers me a little but, as I was already a Pocket user when that happened, not as much as it might because it is actually very convenient). I also like the tools that are available for developers, both within the browser and in the form of extensions. Basically, it is a mighty fine browser that you can rely on, with no ulterior motives driving its development, and all the goodness that comes from being open source.