Rated 4 out of 5 stars

Thank you for this add-on it is useful when you are sending to many addresses.

It will be perfect if:
- The email addresses are drag-and-droppable like in Outlook or Gmail. That way you can very easily move some addresses from To to Cc, etc.
- Like Outlook/Gmail, have a delete button on each email address. So you can remove some addresses very easily.

This review is for a previous version of the add-on (1.8). 

Thanks,

and it won't be perfect :-(
because it would be too complicated to handle addresses as objects in the existing window. I tried... and it would require to rewrite the entire compose window !

If you really want that feature, you can install addon "conversation" (https://addons.mozilla.org/fr/thunderbird/addon/gmail-conversation-view/) : the 'quick reply' mode behaves just like you want !