Thunderbird like Firefox does have about:config settings. But, how the heck do you get to about:config in Thunderbird since there is no address bar to type about:config in. The access to about:config is well hidden: From Tools, select Options…, Click the Advance Tab, select (if it is not already) the General sub-tab and finally click the Config Editor… button. Note: On TBird 3 builds you will get a “This gun is loaded!” warning message the first time (and each time if you don’t disable) you access this option.

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Alternatively, if you don’t want to go hunting through the Options menu, you can get and setup the AboutConfig extension:

1. From Thunderbird Add-ons >> AboutConfig
2. RIGHT-CLICK on the green install now button and select ‘Save Link As…’ . Note: XPI installs do not work yet in TBird, left clicking the button will install the add-on in Firefox.
3. Save the file (aboutconfig-0.6-tb.xpi) to your desktop
4. In Thunderbird, go to the Tools Menu and select Add-ons
5. Drag the file (aboutconfig-0.6-tb.xpi) from the desktop to the Thunderbird Add-ons window
6. When the Install button becomes active click.
7. Click Restart Thunderbird
8. Right-click in an empty area on the toolbar and select Customize…
9. In the Customize Toolbar window, look for about:config button (likely will be at bottom of list) and drag it on to the toolbar where you want it.
10. Click OK when done. Note: Do not click the X as this will not save your changes.