A Thunderbird add-on that allows you to add custom toolbar buttons
The biggest button pack add-on for Thunderbird
Firefox add-on that gives you easy access to about:config.
Provides a button and context menus to easily add a selection or an entire page to YouSticker
Toolbar button to open the about:me page provided by the about:me add-on
A Thunderbird theme with Leopard mail icon
InspectorWidget is an extension which adds a button for invoking the DOM Inspector (DOMi.)
A Firefox add-on that allows you to go to URL in clipboard when the toolbar button is selected.