Montezooma is a Thunderbird Addon that adds zooming functionality to windows.
Sort and search for buttons in (any) toolbar customization dialog
The AutoSlide addon automatically moves the splitter between the thread and the message pane in Thundbird so that the thread pane is set to a optimal height.
Adds darker borders to repeat events to distinguish them from single events.
SortRecipients lets you alphabetically sort the recipients lists (To/Cc) when composing a message, simply by clicking the Sort button, which it adds to the Compose window toolbar.
Use your mouse-wheel to select the next message by placing the mouse over the right hand side of the message list pane and then scrolling.
Enables toggling of Replied/Forwarded states of messages.
Customize the reminder dropdown in Sunbird and Lightning's event and task dialog.
To configure this extension, open the addon preferences from the addons manager.