[ubuntu-uk] new mail notification in system tray?

[Mac]

Apologies if this request about Thunderbird is a bit off-topic, but it 
should be brief if anyone has a ready answer.  I've been googling around 
for days and can't find one.

I'm running Thunderbird 2.0.0.9 (installed via Ubuntuzilla) on Feisty. 
Is there add on or applet to provide a persistent indicator in the 
system tray when there's new mail waiting to be read?

This used to be a feature in T/bird 1.5.0.1x and was visible in the 
system tray even if T/bird was minimised or obscured by another window; 
but ver 2.x seems only to have a transient pop-up when new mail arrives. 
  So if you're been away from the computer, and want to check if there's 
any waiting mail, you can't at a glance.

Any ideas?

TIA

Mac