Rated 5 out of 5 stars

The best piece of protection against .htm and other attachments that cannot be blocked in the TB existing Filters architecture.
Suggest add in .htm to blocked option, then re-open ThunderBird to activate.

This review is for a previous version of the add-on (0.5). 

Thank you for your feedback. I added *.html and *.htm to the default attachments for warning. Should be available in the next couple of hours.