Rated 5 out of 5 stars

Yahoo! Mail Notifier 1.0.4 works fine. I run with FF 17.0.4esr and WinXP SP2. Thanks Michael.

Update on March 18, 2013:

Yahoo! Mail Notifier 1.0.5 works normally. Thanks morac!

This review is for a previous version of the add-on (1.0.4.1-signed).  This user has other reviews of this add-on.