Does what it'supposed to do Rated 4 out of 5 stars
Works nicely and almost perfect. One small bug prevents a message from beeing marked as read when the reply-all button is used (using TB 12).
Also would like to suggest to extend the add-ons functionality to mark messages as read on forward.
Note to the developer: I've adjusted the extension in order to solve the bug and implement the forward behavior. However, I do not find any information on how bugs or feature requests should be filed (no support section on the add-ons webpage). In case you are interested, please let me know...