Introducing a system for separate processes is closest at hand where you for example will be able to run Adobe Flash as its own process and where extensions with stability problems will not affect the browser as a whole. Something Google Chrome has been offering for some time. This is a feature that is expected to be introduced by the end of Q2, I.e. June.
GPU acceleration is another hot topic and here Mozilla hopes to offer Direct2D support in an update for Gecko 1.9.3, slated for October launch. Unfortunately this release doesn’t include the Direct2D acceleration, but will be added later on, but hopefully not that much later.
The next step is Direct3D support, but this is not something it has even put up guidelines for.