How do you install add-ons to Thunderbird?

I am sometimes asked that I could make an extension to install add-ons to Thunderbird easily. AMO says you should download an add-on to your hard disk then install it by the form from Tools->Add-ons menu. Many users may think it is annoying. So, I suggest you a better way.

It is very easy way. Firstly, open a web page in which a link for an add-on you want to install exists by Firefox and open the Thunderbird's add-ons form from Tools->Add-ons. Then, drag and drop the link to the add-ons form. You don't need to download the add-on to your hard disk. I think it is less annoying than the way AMO says.

I tested it on Windows XP. I don't know whether it works or not on other OS.
Anyway, AMO seems to know the issue and work to improve it. Think it as a workaround.