As described by Mary Cooch in http://moodle.org/mod/forum/discuss.php?d=151196
Automatic - this seems to offer that "do you want to open or save this file?" type message. OK...
Embed - this opens up a new Moodle page in which the file is there - Ok..
Force download - this doesn't seem to be any different from Automatic, at least not that I can see
Open - nor does this? Just gives that box asking what you want to do with the file
Popup - this brings up a pop up of your chosen size - and then the same as for Automatic/force download or Open.
(Is it because I am using FF? Is it different for other browsers?)
So could someone explain the differences and why you would opt for one rather than another?