iGoogleBar is a Firefox extension that enhances your Google’s navigation bar by showing the number of unread Gmail messages (only from the inbox) and the number of unread posts in Google Reader.
It is really useful for people who have millions of open tabs, and can’t lose time opening new ones.
The extension comes in .xpi format, so you might want to read our guide on “How To Install XPI Entensions In Firefox”
The extension is free to download and use.
Featured post in Google’s blog: http://googlesystem.blogspot.com/2008/02/more-powerful-google-navigation-bar.html