Firefox 7, released on September 27 2011, uses as much as 50% less memory than Firefox 4 as a result of the MemShrink project to reduce Firefox memory usage. Mozilla Firefox 7.0 is currently the latest stable release.
Couple of new features of Firefox 7:
* Vastly improved memory usage (up to 50% better) and increased speed[43]
* Added a new rendering backend to speed up Canvas operations on Windows systems
* Bookmark and password changes now sync almost instantly when using Firefox Sync
* Added support for text-overflow: ellipsis
* Added support for the Web Timing specification
* Added an opt-in system for users to send performance data back to Mozilla to improve future versions of firefox. This can be enabled by installing an add-on
* Fixed several stability issues