Check the download storage folder in Firefox options, be sure the folder exists.

When I click on "options" I don't see "storage folder" mentioned anywhere in the Downloads section, so not sure what you're referring to?? Just FYI, I have never had a problem opening my downloads before.

If Open and Open Containing Folder in the right-click context menu in the Download Manager window are grayed then that means that the file is no longer in the original download location.
It is possible that your anti-virus software is corrupting the downloaded files or otherwise interfering with downloading files by Firefox.
Try to disable the real-time (live) scanning of files in your anti-virus software temporarily to see if that makes downloading work.

See "Disable virus scanning in Firefox preferences - Windows"

• http://kb.mozillazine.org/Unable_to_save_or_download_files

Thank you, cor-el, for your response! I tried temporary disabling of my Norton of live scanning and still could not open Downloads. I appreciate the link you suggested, but as someone who is not very tech savvy, I go cross-eyed trying to understand the lingo. Any other (easy) suggestions? Thanks again!