"Are you saying those two browsers do not use the adobe plugin? I don't get it."
Absolutely, we are saying that. A few years ago, all browsers used the PDF plug-in. But all the browser makers decided to stop doing that, and make their own PDF viewer/competitors. (The only exception left is the obsolete Internet Explorer). So Adobe has nothing at all to do with your PDF display (assuming the link is followed from a click in the browser).
That said, if I was looking at this problem I'd take a good look at the path name in the browser. Is it what you'd expect? Copy and paste it, change / to \ and %20 to a space. Compare with what you get in a working browser.