I'm very new to Ubuntu so please bear with me. On the latest Ubuntu (12.04) I have set up thunderbird to read my Gmail account. I know there are browser addons that show you how many unread emails you have, but is there a way I can get this integrated with the Unity Mail icon on the top bar?
Not too sure why this is happening but can you please try setting Thunderbird as the default mail client.
Let me know if this worked as I don't have a sure answer but think it has something to do with default applications and would be nice to know.