Hi Kevin,
Thanks for the response. I would consider adapting to Conversations worth of trying if I had 30% of reviews requesting it (I mean all the sources of reviews). In fact this percent is about 10%. Yes, I know that demand of business is more important. Moreover I have business (Multi-User) version of the add-on.
Anyway I do not develop the add-on actively for several reasons. The main of them:
1. This summer Mozilla stopped active Thunderbird development.
2. Outlook provides such features from the box.
3. I do not know how to advertise it. The growth of users amount depends entirely on the fact if Mozilla placed the add-on on featured/new list or not. When it was placed there the user base was growing rapidly. Currently it's stagnated and even slightly decreasing.
Alex
Alex