This is a very promising extension, and quite useful. However, a couple of caveats: 1) There should be an option to make Unicode emojis standard. Quite a few mail programs dislike non-Unicode emojis. 2) The emoticon button currently in the formatting/typing command bar will only allow me to add one emoji. After that it stops working. In fact, the button is so useless that I would like an option to get rid of it. If you could fix the two items above, this add-on would certainly merit five stars. In the meantime, thank you for your hard work so far!
UPDATE: I have changed my rating to five stars after the dev's reply (incidentally, thank you for answering so promptly). The reasons are: 1) If it's on the near-future agenda, that's good enough for me. 2) After researching this a bit, I find that I mistook—what I now discover to be—TB's built-in (and less-than-useless) emoticon button on the formatting bar for one inserted by this extension. Sorry for the confusion. Mind you, I would still like to get rid of it ;-) Apologies again.
This review is for a previous version of the add-on (1.5.7).