If running Firefox on a Debian Linux machine, install virt-viewer:
sudo apt install virt-viewer
Ensure the VirtIO drivers and such have been installed in the virtual machine (if Windows) in order to provide SPICE services.
Then, in Firefox on your workstation:
- go into about:config, and add the key 'network.protocol-handler.expose.virt-viewer' as boolean and set to true
- go into about:preferences, and set "What should Firefox do with other files" to "Ask whether to open or save files".
- in Proxmox, open a SPICE based console for a virtual machine, which attempts a download or a run of a customized .vv file,
- Firefox will then request to open a Virt-Viewer file with Remote Viewer - at this point, you can set it as the default viewer, and it will show up in the application preferences
