Acrobat Reader is a constant annoyance in Safari and even Firefox/Mac. I doubt Adobe did much testing with non-admin privileges, fast-user switching, firefox/safari use, external drives, etc.
How does minimize use of Acrobat, but keep it around for emergency uses? There's no Acrobat option to turn off Safari integration (another sign that Acrobat is badly written), but you can track down and delete AdobePDFViewer.plugin. (Use Spotlight to find it.)
Then find a PDF and make sure it's set to open with Preview (Get Info, etc, etc).
Unfortunately the next time you start Acrobat it may "repair" its Safari integration and reinstall the plugin. I read conflicting reports. I'll document what I learn.
I wonder how much of its software work Adobe has outsourced, and whether they're really getting value from that decision.