Mozilla has recently released the update version of Firefox, Firefox v 39.0. With this build, Firefox for desktop added a new social invite tool for its Firefox’s Hello chat feature, and implemented several improvements and security features.
With v 39.0, Hello users can share the URL with social network contacts, who can join the interaction if they wish so. Before, you need to activate via this page. OS X users should notice smoother animations and scrolling due to implementation of Project Silk, and Google Safe Browsing malware detection is now implemented in OS X and Linux builds.
You can always download the latest build of stable Firefox from official download page.