“As with Firefox, you can extend Thunderbird’s functionality by
installing extensions. Mozilla’s official extension repository has
quite a few nifty tools on offer, and which ones you choose to
install depends entirely on your needs. There are, however, a few
extensions that you might find indispensable no matter how you use
Thunderbird.“Although Firefox and Thunderbird use the same extension format
(and some extensions works with both applications), installing
extensions in Thunderbird requires a slightly different approach.
First, you have to download the extension you want to
install…”