Last week, Mozilla celebrated Firefox’s fifth birthday. It may seem hard to believe that it’s really been that long since Firefox first burst onto the browser scene, but it’s equally hard to understate just how important Firefox has been for the development of the web.

While Internet Explorer is still the most popular browser, holding nearly two-thirds of the market, according to Net Applications, the browser market is much healthier than it was five years ago. There are several major desktop and mobile browsers in active development, notably IE, Firefox, the WebKit-based Apple Safari and Google Chrome, and Opera.

In the months ahead, the browser landscape is likely to see another round of serious shakeup, as these competitors — and other, smaller players — open new fronts in a second browser war. The key battlefields will be access to innovative new technologies, browser performance, security and privacy, and the ability to browse from multiple, diverse devices.