I have been unable to open PDFs from Safari or Firefox since installing Reader X on my Mac (10.6.6). The support page at http://kb2.adobe.com/cps/836/cpsid_83688.html suggests that "Adobe Reader can be confused about which application or version to use in the browser". It gives instructions for repairing Adobe Reader on that page (through the Help menu), but the option suggested was not available on my Mac version.
How can I repair Adobe Reader on my Mac?
After a hugely long saga which has included a complete reinstall of MacOSX 10.6, reinstall of Safari twice, and reinstall of Adobe reader about 5 times. I found out that Safari thought I still had the AdobeReader plugin from version 7.05. At first I couldn't find where this was supposed to be, but it was under the main Library/Internet Plugins (not the one with the exact same name under my username). I dragged the plugin to trash, did one last reinstall and everything now works a treat!
Dear Adobe, SO many customers have similar problems to this, that you gather lots of ill-will. I have certainly wasted at least working days trying to fix this. You need to get your software installation act together so that it properly deletes unwanted files. I have never met an upgrade that caused me such hassle (or only once... and I stopped using that vendor's software as soon as I could)!