Add-Ons which shouldn't be missing in any installation. Make emailing easier and more safety.
Blocks annoying video ads on YouTube, Facebook ads, banners and much more.
Adblock Plus blocks all annoying ads, and supports websites by not blocking unobtrusive ads by default (configurable).
OpenPGP message encryption and authentication for Thunderbird and SeaMonkey.
Google and Zimbra contact sync for Thunderbird. (TB 24 and above NOT supported)
Synchronizes contacts & groups between Thunderbird or SeaMonkey and Google Contacts. Imports Facebook friends, contacts you follow on Twitter, and more.
Automatically fill your address books or send mass mails with e-mail addresses extracted from all your e-mails.