The latest version of Firefox has the following changes:

The address bar now highlights the domain of the website you're visiting
Streamlined the look of the site identity block
Added support for the latest draft version of WebSockets with a prefixed API
Added support for EventSource / server-sent events
Added support for window.matchMedia
Added Scratchpad, an interactive JavaScript prototyping environment
Added a new Web Developer menu item and moved development-related items into it
Improved usability of the Web Console
Improved the discoverability of Firefox Sync
Reduced browser startup time when using Panorama
Fixed several stability issues
Fixed several security issues
Please see the complete list of changes in this version. You may also be interested in the list of changes in the previous version.