An often reported problem:
Opening or closing a PDF with the Adobe Acrobat plug-in
demands 100% CPU time of the processor (one core).
Detailed description, cause and solution:
http://public.ok2life.com/welcome/index/54.html
The solution worked fine for me (XP, Acrobat Reader 8.0, Firefox 2.0.0.1)
I did:
1. Exception for AcroRd32.exe in the Windows Firewall
2. create the empty directory WWW_OpenURL in
C:\Documents and Settings\<currentUser>\Application Data\AdobeUM
and the PDFs which used to hang work fine now.
Regards to 'David', author of the aforementioned article.
Hope this helps others as well...