It has been only recently that I am getting a message on my screen while in email.  The message says: "Email Defender cannot work.  If you keep seeing this message, click here  for more details.  When I click on the here link, a download tab appears on the bottom of my screen.  When I click on the download tab, I get: "Select an app to open this .xpi file, and it offers, Notepad, Opera Internet Browser, VLC media player, Windows Media Player Legacy, and Word.  None of the options work to show me a resolution.