Rated 5 out of 5 stars

Bumping up Justin's comment so people know HOW to make it work for Firefox 3:

by Justin on June 26, 2008
For this to work in FF3, you just need to modify the xpi file. Click the "Ignore version check" link and then right-click on the Add to Firefox and select Save Link As. Open the XPI file with WinZip and then open the install.rdf file with a text editor. Change line 24: "2.0.0.*". I changed 2.0.0 to 4.0.0. Then save it (you may need to refresh the file in the archive). Once you've done this you can reinstall the add-on and it works perfectly.