AutoNotification Whatsapp Desktop blank

I use Whatsapp Desktop in Firefox on my old Vista OS Dell Studio in conjunction with more regular use on my Samsung Galaxy S6. Most of the time it work well then, fo no apparent reason just goes blank. The window opens when I click on the Desktop icon but there is nothing there. I can access the chats OK on Whatsapp Web. I've "logged out from all computers" on my phone and reinstalled with the QR scan but still can only get the Whatsapp Web.
Once or twice in the past the QR code has appeared in the Whatsapp Desktop window so I've been able to get it functioning again that way, but that is quite rare - usually it just stays blank.
Would be most grateful for a little help.

 

I'm probably in the wrong place. This forum was the top of the list when I searched for Whatsapp query forums.