What exactly is a portable app? Well, in Windows, it basically means a version of an application that doesn’t need to be installed to a particular folder, doesn’t need to write entries to the Windows registry, and typically doesn’t show up in the Add/Remove dialog. So you can install portable applications to a USB flash drive and take them with you to use on any computer.
But you can also install a portable application like Firefox 3 beta 5 portable edition to any folder on your hard drive. Why would you want to do that? Because then you can try out the latest test version of Firefox without overwriting any of your Firefox 2 settings. The down side is that Firefox portable edition will not import any of your Firefox 2 settings automatically. But you can use programs like the Firefox Environment Backup Extension to copy some of your settings.