Rated 4 out of 5 stars

This add-on is almost great. You can easily setup templates to reply to emails with custom fields [to: firstname] etc. But there is no way to add attachments to templates...at least not that I can find. Version 0.9.12 is supposed to have these "Pro" features merged in but it seems to have been left out.

This review is for a previous version of the add-on (0.9.12). 

The next version is still pending for review at mozilla ...
You can get it here: https://bugzilla.mozilla.org/show_bug.cgi?id=1391020#c63

The new version (1.0) including the pro features has passed review a couple of minutes ago.