It's barely a long time since Firefox 4 came out. Remember the fast-release cycle? Well, the next version is out in beta. I've started using it.
What's new, you ask? Well, nothing much for now. Don't expect big new features or interface changes anytime soon. The fast-release cycle means quick performance patch-ups and security updates. New features will come out slowly.
The beta 2 of Firefox 5 currently looks almost no different compared to the previous version. The Do-Not Track feature is more obvious to users now. And like Google Chrome, it is really simple to change 'channels' in Firefox from the About window now.
Firefox for Android is getting the Do Not Track option in the new version.
You can try out the beta version from over here.