I had the same exact problem. Here's how you solve it:

Tools > Options > Applications Tab > And then under "actions" switch from "use Adobe in firefox" to "use adobe reader (default)"

This should solve the problem.

I am running Adobe Acrobat Pro and it does not have and "Options" tab under "Tools." One of the Adobe tech support guys got back to me on this issue, and he said that since Firefox has so few MAC users, they do not offer support to MAC users. So, I read the reviews on CHROME, Google's browser, and I downloaded that and it works GREAT! Chrome solved the problem! I no longer use Firefox, but I did try to make the repair you suggested in case I want to use Firefox, but I don't have the tabs you are suggesting. Thank you for taking the time. You put more effort into this than Firefox support did.

If anyone else is looking at these answers, please ignore Mr. Ross's misleading response and suggestion to move on to Chrome.

Deejay17 is referring Mr. Ross to the browser menu item, Tools>Options>Applications and advising that the "use Adobe in Firefox" be changed to "use Adobe Reader (default)". Please note, deejay17 gives the right answer, however, while this helped me with 3.5, but I have the problem with 3.6 and cannot resolve it. It now hangs on the first few openings of pdfs, then inexplicably is not a problem until I want to close down.

Mr. Ross's reply should be removed since deejay17 answers the question and Mr. Ross failed to try his advice. There is no need to refer people away from Firefox. If you didn't know how to use a refrigerator would you tell people not to use one? I do not object to the moderator removing this reply also as it would be superfluous once Mr. Ross's response is removed.

To DMCFF1, you obviously did not read my response. I did try it. I do not have an Options tab under Tools. You are making an incorrect assumption that I did not bother to try it.

My post is most valuable not only for Firefox users but also for Safari. A friend of mine was complaining about how slow Safari is, and while I was there he downloaded Chrome and fired it up. It was like 10 times faster. He has thanked me several times. BTW I do not work for Google nor do I have any interest in promoting Google products. I stumbled upon Chrome accidentally and have been very happy with it since.

Your condescending tone is also noted. Please be assured to know that I in fact do know how to use a refrigerator, and I do know how to use a computer. In fact, just to be sure, I just fired up Firefox and looked again under Tools. I DO NOT HAVE AN OPTIONS option under this TAB. I have looked for another Tools tab or subcategory under other tabs and cannot find one. So please do not assume I am absolutely incompetent.

The equivalent of "Tools > Options" on the Mac is "Firefox > Preferences"

http://kb.mozillazine.org/Menu_differences_in_Windows,_Linux,_and_Mac

Hi Tony, I appreciate you sending me this info. What you write makes sense. I followed this path Applications>Content Type>Action> but the only Adobe option under Content Type is "Adobe PDF document." I can change the Action from "Always Ask" to "Use Adobe Acrobat Pro," that seems to be my only option, unless you think I am completely following the wrong path. Thank you for looking at this. I would like to have Firefox running as well as it can even though I've switched browsers.