Majority of changes in Firefox 5 were just bug fixes, while, Firefox 6 is planned to have more HTML5 and CSS3 features. On the other hand, 7th version of world known Internet browser will concentrate on performance improvement and memory usage optimization.
All those memory optimization options will be even more extended in Firefox 7 that can also reduce the original RAM size of the browser. Changes of some algorithms will also have performance enhancements to a browser with lots of sites viewings at the same time for quite long time period, for example, couple of days.
Firefox 7 can be found through Aurora channel where it should become available for download today.