Thunderbird add-ons that I've either used for years, or tested and highly suggest.
This addon adds month tabs into Lightning calendar month view
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.
custom additions to Stylish extension.
brings back features from 0.5.9 and adds new features
I can't be bothered to change SC, so amo will allow it to be uploaded
Adds a summary of mail accounts and folders to replace the account central pane and the empty folder preview
The main goal allows users to open (and in some cases edit) page source with external applications.
Zoom in, zoom out, and reset zoom with one toolbar button. Works in the Compose window too.
(Formerly Local Install) The primary goal of this extension is to provide the tools needed to install and manage extensions and themes locally and tons of other features.
Note: With Toolkit 6.0 Auto Archiving is fully working in Firefox 2.0 and temp...
This add-on provides a follow-up email feature for Thunderbird.
Maximize message pane by collapsing the thread pane. You can read a message in larger area without opening a new message window...
Allows you to configure a set of WebApps to open easily as tabs within Thunderbird trying to give them all the functionality that you'd find in Firefox.
Adds a new action to mail filters to allow playing a particular sound when the filter matches. Also includes several sample sound files.