Hello, to manage how to view your PDF files, I recommend you visit the following link and carry out the procedures detailed there, one of them may help you solve your problem. View PDF files using Firefox’s built-in viewer

I appreciate your response, but as I indicated I have already done most of this. Adobe Acrobat is set to be my PDF reader, however, Offidocs opens anyway. I would like to avoid refreshing Firefox so I don't have to go thru the process of re-installing all the add-ons. If I completely re-installed Firefox what would that entail and what steps would I need to follow to keep Offidocs from re-installing before I can make sure Acrobat is checked again? I never installed Offidocs in the 1st place. It must have come with another program like IrfanView, from an earlier version of Windows 10. Thank you.