The Differences Between Gecko and Servo

Almost everything that involves a DOM API has to be implemented again. Canvas, it's a special case too, because not only is it a DOM API, but it actually is also a vector rasterization engine. Gecko and servo do completely differently. They share a web content rasterizer, but the vector rasterizer is different. In general, CSS is much easier to rasterize on a GPU than a vector in Canvas.