When you choose Open, Firefox still has to download the file, but usually it will delete it later automatically. If you do not want the Desktop used as a transitory TEMP folder, unfortunately, I don't know of a way to choose a "real" temp folder, but it may at least be less distracting to change your default downloads folder from the Desktop to a different folder. You would make that change on the Preferences page, general section. Either: * "3-bar" menu button > Preferences > General * Firefox menu > Preferences > General * type or paste about:preferences in the address bar and press Return If you normally have Firefox set to "Always ask me where to save files" you can temporarily set it to "Save files to" to choose a different folder and then change it back. As a Windows user, there's no way for me to test any of this myself...