The title is inaccurate - Instantbird is a project independent of Mozilla which has been around for a long time.
An Android version of this would be nice. I have only found instant messaging apps for Android that has a centralized model. I give all my passwords (Jabber, Facebook, Live Messenger, ICQ, AIM) to a third party that acts as gateway. I'm not comfortable with that.
The icon definitely does not make me think IM client, but MUA.