How do I make firefox automatically open downloaded files rather than save them?

I am using a portable version of FF3, and every time I try and download any file it makes me save it. This is a problem because I want to keep all of the files on the flash drive, and not load any of them onto the computer. When I go to Tools:Options:Main it only gives me the option to always save to the same folder or asks if i want to choose the folder every time. Google provided me no help, so I have hoping a Firefox savvy Flutherite might be able to help me.