Could you describe this in a little more detail? First, are you opening PDF documents from a website? If Firefox is automatically downloading them instead of displaying them, you may be able to change that setting. Please see this article for more information: [[View PDF files in Firefox without downloading them]]. Second, instead of clicking items on the download panel to open them, try clicking the folder icon on the right to open the folder they're in with the file highlighted. What kind of file does Windows say it is? If you right-click the file, do you have the option to open it in another program? Third, if the problem comes after printing, make sure the checkbox for "Print to file" is NOT selected in the print dialog.