Rated 5 out of 5 stars

yazan: iluvtolaff tarih: Eyl. 28, 2011 ·

He just made a new version and it's working for me so far! Go here to install (click on "Install Yahoo Mail Notifier" under 'Quick Start' in the right sidebar).

http://ymnotifier.mozdev.org/index.html

This review is for a previous version of the add-on (1.0.0.21.1-signed.1-signed).  This user has other reviews of this add-on.