Just to confirm I understand this, you have Firefox set to open PDFs outside of Firefox in Acrobat Reader DC.

(This article has the steps for changing from Firefox's built-in viewer to a different viewer, for quick reference: View PDF files using Firefox’s built-in viewer)

When you try to open or download the EDF PDFs, what happens -- do you get an error message, blank tab, etc.?

Hi jscher2000 and thank you for the response. When I try to Access, open, or download a PDF in Firefox, using Adobe Reader DC from EDF only, I get a blank page. I have no problems accessing Adobe Reader PDF's from other websites.

I think the common pattern when you have set PDFs to open in an external application and the set normally uses a separate window/tab, is that Firefox would open a new tab briefly, then detect that the PDF should be downloaded and close the blank tab. So... what could be interrupting that process?

If this is a link or button, make sure to simply click it and not divert it using Ctrl+click or right-click > Open in New Tab.

Do you have the redirect warning turned on? That feature sometimes leads to invisible blockages, so if that is turned on, I suggest turning it off here:

"3-bar" menu button (or Tools menu) > Options > Advanced

On the General mini-tab, in the Accessibility section, make sure to uncheck the box for "Warn me when websites try to redirect or reload the page"

If that's already off, could you check Firefox's Browser Console to see whether there are any error messages? Here's how:

Before clicking the link to the PDF, open the Browser Console using either:

• Ctrl+Shift+j
• Developer menu

Click the "Clear" button at the top. Leaving that window open, return to the page and click the link/button to get the PDF. After it finishes not working, flip back over to the console and check for any new messages. Anything?

Hello again jscher and thanks for your ongoing support. I have found the cause of my problem to be the installation of the new Adobe Reader DC. The new Reader now immediately downloads all new PDF's to Libraries > Downloads. Previously, (under Adobe Reader XI and previous versions) this process had to be physically carried out. I rarely visit the Downloads source, so missed it. Reader DC is now a very complex programme and i will need to study it further. Thank you for your advice and I apologise for what amounts to a waste of your time.