When I open a PDF file in Firefox, I just get a blank page.
We've seen this with Acroread 7.
In Firefox, suggest that you disable the automatic filetype plug-in handling for PDFs (Edit, Preferences, Downloads, Plugins, PDF, unclick Enable) and have Firefox opening PDFs in Acrobat Reader (/usr/local/bin/acroread) by default. This causes the document to open in a new window.