@John- Please update Firefox support page!!!!!

While looking through the Firefox 3 Portable option pane in the "Applications" tab I noticed that "mailto" links are now set as a "mimetype" so you can use Thunderbird Portable for mailtos. I set it up myself. I just went to the aforementioned panel went to "mailto" and chose "Thunderbird Portable.exe." It works. I tried it on a couple links.