Rated 5 out of 5 stars

Enfor, to acquire the add-on, right click on the download button (not left click as you would for a normal download. This will give an option "Save link as". Then save it to a folder on your computer i.e. Download where you will remember it. Then go into the Add-on page for Thunderbird (or whatever program you are trying to add this to. There will be a gear icon near the top right of the page. Click on that and selct Install add-on from file. Then tell it the location where you saved it.