Do you have Firefox set to use the Adobe Acrobat plugin? It looks as though it might be missing or disabled, since it is not shown in your "More System Details" (next to your post). Could you check on the Add-ons page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. Then on the right, look for Adobe Acrobat. It may be at the bottom on a grayed background.

If you do not have it: Make sure it is not your preferred viewer here:

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

You can type or paste pdf in the search box above the list after it loads to filter it.

If you do have it but it can't be enabled using either "Always Activate" or "Ask to Activate": You may need to update. I recommend using the Help menu inside your Adobe product (Reader or Acrobat) to Check for Updates.

Any progress?

Thanks for the help. When I followed your directions and went to "applications" under "tools," I realized that I had never actually installed acrobat reader at all.  :/. Firefox had been able to still open PDFs somehow in a new tab up until recently; I don't really understand how. Anyway, I downloaded it, and everything works now. Thanks again.

Current Firefox versions have enabled a built-in PDF Viewer that doesn't have all features that other PDF readers like the Adobe Reader have or may not function properly otherwise.

You can change the action for Portable Document Format (PDF) from Preview in Firefox to use another application like the Adobe Reader or set to Always Ask in "Firefox > Options/Preferences > Applications".

See also:

• https://support.mozilla.org/kb/view-pdf-files-firefox-without-downloading-them
• https://support.mozilla.org/kb/disable-built-pdf-viewer-and-use-another-viewer