I'm currently using Firefox 8, and I am reasonably happy with that version of the program. However, I see that since it was installed on this computer, Mozilla released version 9, then 10. Is there a compelling reason to upgrade Firefox 8?
The latest version of Mozilla Firefox is 11 and it was released on the 13th of March. There are multiple reasons why it is better to use an up-to-date Mozilla Firefox version, but this depends only on your preferences and needs. Mozilla Firefox 11 is wrapped in a wide range of features, such as Google Chrome migration, SPDY integrated services, Page Inspector Tilt (3D View), Add-on Sync, Redesigned HTML5 video controls, and a Style Editor (CSS). If you care about the looks, it is good to know that its interface is also a bit changed. A complete list of changes can be found here http://www.mozilla.org/en-US/firefox/11.0/releasenotes/
