This app saved me time and a reboot. I kept getting a "A copy of Firefox is already open" messages after a hang and force quit, though the application didn't show up in the list of what was running. A Google search told me which hidden profile file was creating the problem, but I didn't really want to switch hidden file view on for the entire machine from the terminal. Houdini let me find and delete the file and get my browser back up and running without rebooting the machine. Thank you, thank you, thank you! (The machine is running Snow Leopard, and the download provided here worked just fine.)