hello, please see Where to find and manage downloaded files in Firefox

I can open the downloads window that shows me all my downloads but the "open" is not bold and it won't allow me to open the file.

if you cannot open the files this way then you've probably not chose to save them but only to open them initially (which will put them into a temporary directory, open it with the pdf viewer you're using & removing the files afterwards at some point).

what you can try now is to right click the files, select copy download link and then paste that into the address bar of the browser to reinitiate a download.

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 and they may have been removed by Anti-virus or cleanup software.

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