Rated 4 out of 5 stars

Went near crazy trying to install. PC kept telling me never heard of an XPI file. Then saw alienfromzog's review (copied) below

-How to Install
by alienfromzog on June 16, 2008
Installing is actually really easy just not well explained.

1. Download the add-on to your desktop.

2. Open the Add-on's window from Tools on the Menu bar

3. Simply drag-and-drop the download into the Add-on's window

4. When instructed restart Thunderbird.

AFZ

Haven't really tried it yet as a working dictionary but it can tell colour from color!

Insxtalled just fine - hope this helps others

This review is for a previous version of the add-on (1.19).