Rated 5 out of 5 stars

WORKS, and and that includes the British version as well.

SOLUTION:
You can't use the [download-button] to add the dictionary file to your programme. Or in my case, a new clean thunderbird (ver 31) install.

Give the developers a break, it does all work, but sometimes you have to work at it to get it right. If the button doesn't work, then right click it and download the file->link to a directory.

Go to the add-ons manager, and select install from file (do it from where you saved that *.xpi file)

Accept all warnings. Restart the programme, and - volar' - you now have your spell-checker installed.

Very useful, and free, and just brilliant.

This review is for a previous version of the add-on (7.0.1).