Mozilla is rolling out Firefox 12 stable edition to all the users on older versions. And they have also released Firefox 13 in beta.

Major changes from Firefox 12:

NEW
When opening a new tab, users are now presented with their most visited pages
NEW
The default home page now has quicker access to bookmarks, history, settings, and more
CHANGED
SPDY protocol now enabled by default for faster browsing on supported sites
CHANGED
Restored background tabs are not loaded by default for faster startup
CHANGED
Smooth scrolling is now enabled by default
DEVELOPER
72 total improvements to Page Inspector, HTML panel, Style Inspector, Scratchpad and Style Editor
DEVELOPER
The column-fill CSS property has been implemented
DEVELOPER
Experimental support for ECMAScript 6 Map and Set objects has been implemented
DEVELOPER
Support for the CSS3 background-position property extended syntax has been added
DEVELOPER
The :invalid pseudo-class can now be applied to the element
DEVELOPER
The CSS turn unit is now supported

Firefox 14 is also out for the users on Aurora build which is updated much faster and is pretty close to nightly releases.