Get Label-Specific Notifications for Gmail in Firefox

[Exterminator]

It's called Gmail Notifier Restartless. After installing the extension you need to go to options page. There is a box named Gmail Feeds, to which you can append this string at the end of the box:

https://gmail.google.com/gmail/feed/atom/label

The label is the name of your label for which you want notifications.

 

[McLovin]

I see no point in this if you have the Google Talk Messenger because when ever an email does come through it pops up saying what it is.