We are hearing plenty about Firefox 5, which should become available as a beta browser next month. There has not been much news, however, about the Firefox core and how it would change to deliver the ongoing performance improvements Mozilla outlined in its Firefox roadmap in February.
Mozilla also said that it is making changes to its Gecko rendering engine. Project "Azure" targets the creation of a new 2D graphics API for Firefox as well as new 3D backends to accelerate content rendering to OpenGL, Direct3D 9, and Direct3D 10. When implemented, we should see much more efficient hardware acceleration performance that works across all popular OS platforms, including Windows XP.
Firefox 5 may receive some new features, but Mozilla was pretty clear when it stated that this work is very much in the starting phase. Firefox 7 and 8 are better bets to expect IonMonkey and Azure.