Changes
→Silent installation of Thunderbird extensions
* download the extension
* go to "%PROGRAMFILES%\Mozilla Thunderbird\extensions\" and see what folders you have there
* install the extension into Thunderbird manually (this needs an explanation as to how this is done, - is it by copying the .XPI file into a Thunderbird sub-this directory? or using Tools -> Extensions -> Install from within Thunderbird?)
* you will notice that the additional folder appeared in "%PROGRAMFILES%\Mozilla Thunderbird\extensions\" - this is your new extension
* copy the new folder to the server