Thunderbird add-ons in this collection I am trying out, but don't yet have enough experience with to endorse.
Allows bidirectional access to Google Calendar
OpenPGP message encryption and authentication for Thunderbird and SeaMonkey.
Access to Google contacts and synchronize them with Thunderbird address books.
Adds toolbar buttons to the customize toolbar window in several programs including Firefox, Thunderbird and SeaMonkey. Some of the buttons make commonly preformed actions quicker, others add new functionality.
Displays the address books in a sidebar in Thunderbirds 3-pane-window and can be toggled with the F4 key or a toolbar button.
Visit my Contacts Sidebar site for recent versions and news.
Note from Mozilla: This add-on has been discontinued. Try Menu Icons Plus instead.
Adds icons to all menus along with some other features...
The "Swiss army knife" of folders. Turn your favorites into tabs - open folders and subfolders, move mails without scrolling around or searching. powerful + easy.
See new mail at a glance after automatic filtering - supports quickFilters addon!
Google and Zimbra contact sync for Thunderbird. (TB 24 and above NOT supported)
Facilitates handling of duplicates in your address book(s). Allow to search and remove similar contacts.
Thunderbird Message Filter Import/Export is a thunderbird/mozilla extension to import/export message filters.
Automatically fill your address books or send mass mails with e-mail addresses extracted from all your e-mails.
Adds many new mail filter actions - launch a file, suppress notification, remove star or tag, mark replied or unread, copy as "read", append text to subject.
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