Rated 5 out of 5 stars
Excellent Add-On, absolutely indispensable for me! Now I don't have to use yucky Word-Copy/Paste to try and produce highlighted text in emails anymore ;)
Anyway, I found out why the highlights are not shown in Outlook, see here: http://pages.citebite.com/k7f4e3t5ugne
As a workaround, I removed all occurrences of " !important" (minus the quotes) from the file "overlay.js" in the extension's folder in the Thunderbird profile folder.
Thanks a lot for your investigations, I'll publish a new version with your modifications soon.