In my Nightly Tester Tools entry I talked about using this extension with Firefox. The newest version 1.2 works with Firefox 2.0b1-3.0a1 plus Thunderbird 2.0pb1 (pre-beta)-3.0a1 and SeaMonkey (former Mozilla Suite browser) 1.5a.

The installation for Thunderbird is a little more complicated since it doesn’t do the automatic XPI install like Firefox:

1. Go to the Nightly Tester Tools site
2. On the bottom right of the page RIGHT-CLICK on the Install Latest Version button
3. Select from the context menu ‘Save Link As…’
4. Keep the default file name (nightly-1.2.xpi), but save it to the desktop
5. Minimize Firefox
6. Toggle to Thunderbird
7. From the Tools Menu select ‘Add-Ons’
8. Minimize Thunderbird (note the Add-Ons window should still be on the desktop)
9. Drag the nightly-1.2.xpi file from the desktop and drop in the Thunderbird Add-Ons window
10. Follow the instructions and then once the install is done, restart Thunderbird
11. Drag the nightly-1.2.xpi file into the recycle bin

Now you have the ability to get your favorite extensions working again in Thunderbird 2. As with Firefox though, forcing some extensions to work with Thunderbird 2 can result in odd behavior and broken main window. Use at your own risk.