I have opened the URL indicated, downloaded a file named
smarttemplate4-1.3.1-tb+sm.xpi, and tried to follow the
instructions, which say:
1. Download and save the file to your hard disk.
2. In Mozilla Thunderbird, open Add-ons from the Tools menu.
3. From the options button next to the add-on search field, select
"Install Add-on From File..." and locate the downloaded add-on.
Since there is no "options button" in the Add-ons submenu, I failed
to follow the third instruction.
I use the Linux version of Thunderbird. Is it possible that the
Windows version has such a buttin in the Add-ons submenu?
But thank you anyway.
Bye,
Wolfgang