pinning desktop icon into 'plank'
I use 'plank' as a row of desktop icons in fluxbox on debian 8, but I wasn't able to pin the icon, i.e. 'lock' it so that it was available even when closed. So with the guidance of the plank developer I've created a pin for it by -
locate Vivaldi.desktop cp /usr/share/applications/vivaldi-stable.desktop ~/.local/share/applications/vivaldi-stable.desktop
Open 'vivaldi-stable.desktop' in leafpad and append
to the end.
Close vivaldi and then reopen it, and you can pin it in plank.