Well, that did not take long! Firefox 5 was officially released only yesterday and today the Ubuntu 11.04 repository has been updated with Firefox 5.
Generally the major releases of Firefox (or any software for that matter) are not included in the main repository (except for than the LTS) and if they do gets included, it takes a lot of time. Firefox 5 is not very different from Firefox 4, which is already there in the repository. That might be the reason for Firefox 5 being available so quickly.
So, users of Ubuntu 11.04 “Natty Narwhal” do not need to add any extra repository to install Firefox. All that you need to do is update your system as usual.
$ sudo apt-get update
$ sudo apt-get upgrade
If you do not like the command line interface, you can also update using the Update Manager. Click on Check and after it has finished checking, click on the Install Updates button.
Firefox 5 is available in the main repository only for Ubuntu 11.04. So, those who are still using previous versions of Ubuntu will have to add the extra repository to upgrade to Firefox 5 as we have mentioned here.
The jump from Firefox 4 to Firefox 5 is very small compared to, say, that from Firefox 3.6 to Firefox 4. So, those who are already using Firefox 4 should not face any problem after upgrading. Firefox 5 brings some new feature such as Do-Not-Track and has better performance and handling of CSS animations. You can read our review of Firefox 5 here.