Telemetry in Firefox
One of the big challenges in developing a great Web browser is figuring out where the browser's performance gets in the way of people using the browser. As Nicholas Nethercote notes, you lose more when you're slow than you gain when fast. That means that a top priority for Mozilla is to not just work on increasing overall performance, but to really hone in on the areas where we're slow and make sure we speed them up.
Unfortunately, the traditional tools for measuring performance, various industry standard benchmarks like SunSpider or our own "ts" start-up time tests, don't really do a very good job of measuring when we're slow. What we really need to measure in order to tackle our slowest code is real-world usage and that requires an entirely different way of thinking about performance.
Telemetry in Firefox is a new technology that allows our developers to build performance tests right into Firefox itself and to have those tests running while users are interacting with Firefox and the Web.