CentOS - Mar 2019 - Firefox view downloads folder - changed program

Hi All,

A short while back, Firefox changed from using (I believe) Dolphin to using 
gwenview when I choose 'view in container' or 'view all
downloads'.

The  problem with this is that when I choose 'view in containter' it no
longer
selects the appropriate file.  Does anyone know how to change it back?

I'm using C7 with KDE

Gary