Hi Peter,
On my machine IE behaves the same as FireFox - in other words, the PDF is opened directly in the browser, no questions asked.
So in your case the fault is either in the client machine (ie PDF not installed into the browser maybe, or a setting that forces it to save, not display, PDF files) - or on the server side you are explicitly telling the browser to "not display" the file. This is usually done with the content-disposition header, and in the File Downloads example you'll see a line of code which does this. In your case I'm thinking you _don't_ want to use this line of code.
the way to test which end is having the problem is to
a) try the server from different machines - including putting the server online so we can get to it from here and let you know what happens and
b) try from different browsers on your machine. Firefox respects content-disposition as well, so you should see the same behaviour in all browsers if the problem is in the server side.
cheers
Bruce