The changes most graphical in nature (SVG, Canvas, XUL2D) depend on a switch to the cairo graphics library as the fundamental display architecture for Gecko, work on which is already well underway. The aim of shifting to cairo is to bring modern, hardware-accelerated 2D graphics capabilities to the whole of the web, without requiring proprietary plugins or rendering obsolete the broad and rich set of web authoring techniques developed over the past decade.
The layout changes -- see also the "XUL' and XBL2" section of this roadmap -- center around David Baron's [[Gecko:Reflow_Refactoring|"reflow branch"]], the aim of which is to eliminate reflow commands and types, and significantly reduce the complexity of the Gecko layout model. This is the first change to global layout architecture in several years, and it is hoped that it will address many problems related to incremental reflow. In addition, it should simplify some problems that are not practically soluble with the current architecture, such as support for inline-blocktable.