Firefox's rendering architecture has changed quite a bit in the past few years. Web content is becoming more and more complex, while we still serve it on very low end devices such as mobile platforms where expectations are very high. Gecko's compositing system moved to an asynchronous architecture allowing us to keep some parts of the user experience perfectly smooth even when the the browser is busy processing web content such as JS. Among the elements that benefit from this: panning, zooming, CSS animations and transitions, video playback. This talk will give an overview of this asynchronous architecture, How it impacts user experience and what we want to achieve in this area in the future.