Have your temporary Webkit files disappeared from your
/tmp folder? Perhaps you should be looking in your
/var/tmp folder instead. Recently Firefox and Safari seem to store flash temporary items in a new location. Look in
/var/tmp/folders.501/TemporaryItems. (This assumes that your user id is 501, which is typical but not certain–type
id at the command line.) Instead of being named “Webkitplugin”, the file will be called something like “TemporaryFlashItem”.