TechTree: Enhancements that are supposed to arrive with new version are:
Enhanced three-state-UI for Do Not Track.
This time around, Firefox would auto-suggest the ways of improving application startup time.
Mozilla would use FHR (Firefox Health Report) to help improve performance, fix problems and let users see how their browsing experience compares against other instances of Firefox.
Apart from the new aspects above, Mozilla is expected to have implemented various graphics-related performance improvements and bug fixes.