Rated 5 out of 5 stars

I was finally fed up with trying to read the diffs I get in my inbox and went in search of a tool to provide some syntax highlighting, worried I might have to write my own and to my delight this was here. The icing on the cake was that this also provide side-by-side diffs, superb!

This review is for a previous version of the add-on (0.6.2010.06.25.16.16.59). 

Well if you want to be a maintainer of this plugin, go ahead. The original author no longer works on it, and I have not used Thunderbird in a month now (plus most of the diff mails I receive are colored HTML to begin with).