Why won't PDF files open anymore?

Linc, I'm writing now to you from a different computer. I shut down my iMac and after letting it sit for a minute or two I started it up again, immediately pressong the command-r keys and released them wnem the spinning dial appeared. After quite a time, the screen changed to the plain gray backdrop of my regular startup page, but a Mac OS X Utilities window appeared in the center of the screen. Nothing seemed "operating" for quite some time so I inserted the OS disc into the optical drive. Still no "activity" and no way to eject the disc. After another period of time Utilities window finally came alive and offered me the opportunity to click on the Install Lion option. After agreeing to the terms and condityions the system offered me two places to install it: the Recovery HD or the Macintosh HD. But the Recovery HD is locked and only the Maqcintosh HD is available to select. I'm hesitating doing anything until you tell me I'm on the right track and should, indeed, select the Macintosh HD dirve. Yes?

Thank you. Approximately 1 hour and 27 minutes to accomplish the download from iTunes and then my "system will restart automatically." I'll get back to you then.

All reinstalled. (Of course when everything reopened I was able to eject the Mac OS X Install DVD I had placed into hte optical drive.) But...no change in my problem. The .PDF files I keep on my desktop open just fine, but the URLs imbedded in an email still go to the URL page, but no image opens. Grrrr.... Now what?

I will schedule this appointment BUT...EVERY time I've scheduled an appointment with a "Genius" at my local Apple Store they have been UNABLE to solve ANY problem I've ever brought to them (on 4 different occasions)! I fear this one will be no different, but we shall see and I'll fill you in after the visit. I really thank you for the extensive help you've given me. I really don't think anyone at my local Apple Store will be anywhere near your knowledge and capabilities! Thanks, Linc.

I was standing in the Genius Bar line awaiting my appointment when your email arrived. I was able to demonstrate all my problems to my assigned Genius, Herbie, in real-time (using Firefox). I told him it was the same in all user accounts as well as no matter whether I used Firefox or Safari. He switched to Safari and voila, everything worked perfectly. The imbedded .pdf files from the email that hadn't opened in Firefox opened in Safari AND the PDF Preview and Print views in Safari worked where they were not working in Firefox. We switched back to Firefox and now the imbedded .pdf files in an email opened, but the PDF Preview and Print views were still weird. So now I at least have a workaround - simply switch to Safari if Firefox isn't cooperating. (But this may just get me to go back to Safari as my browser of choice with my iMac after all! Do you know of an easy way to sync my Firefox bookmarks with my Safari bokmarks and vice versa so that they are essentially mirror images of one another?)

We concluded our session by deleting the one remaining AdobePDF item in my Internet Plug-ins Library, but we couldn't observe if that did anything or not.

Herbie's conclusion is that whatever my problems were/are, they are not Adobe or Apple problems, but they're probably Firefox issues. So I guess I'll report this to Mozilla to see if anyone else has experienced it and to see if they can fix it.

Thanks for all your time and effort to help me with this issue, Linc.