Some nice tools for Thunderbird 3+ users, Chatting and Email/Webmail.
Add support for chat protocols implemented in libpurple.
Adds a column for displaying the certificates Email address to the "Your Certificates" tab of the Certificate Manager
NO LONGER MAINTAINED.
Automatically inserts HTML signatures into your Gmail messages based on which address you are sending from. Maintain up to four signatures per address.
USE BETA VERSION: http://goo.gl/FdyXq (v1.18.6b)
Note from Mozilla: This add-on has been discontinued. Try Add-on Update Checker instead.
Notifies you when updates are available for your extensions and themes.
Maximize message pane by collapsing the thread pane. You can read a message in larger area without opening a new message window...
Based on Gmail Manager by Todd Long. This fork is intended to a supported version of Gmail Manager since Todd appears to have gone MIA. Manage multiple Gmail accounts and receive new mail notifications.
Type in accented letters, international characters or symbols into Firefox or Thunderbird, either simply by using a context menu (there being support for many languages), or quickly by keyboard macro (you can even define your own).
Selects an identity based on the recipients list when sending an email
Change priority of the received messages from the toolbar button and the context menus...
Protects you from phishing attacks by verifying the From: address domain name of emails as you read them. Sender Policy Framework (SPF) and DNS-based reputation lists are used.
Email Bookmarks are here ! ... eMark your important emails.
Do you have an email that will need to revisit/attend later on ? Would you like to keep it handy and get it with a simple click ? Bookmark your important emails with the eMarks addon.