Recently a comment was left on my Get Mail Extension stating the add-on was no longer on AMO (addons.mozilla.org) and provided a link to his Toolbar Buttons extension. Once installed and you restart Firefox (SunBird, Flock or Thunderbird) right-click on the toolbar and select ‘Customize…’ , you will discover a treasure trove of new toolbar buttons. Simply drag and drop the buttons to your toolbar. Important: be sure to click ‘Done’ when finished. If you click the X instead, your changes will not be saved. A couple buttons I found useful were Undo Close Tab and Check for Update (much quicker then going through the Tools menu).
The extension works with the following applications:
- Firefox 1.5 to 2.0
- Thunderbird 1.5 to 2.0
- Flock 0.4 to 1.5
- SunBird 0.3 to 0.4a1
Tip Source: Michael Buckley
The Firefox Extension Guru's Blog 