I wrote an article just a few days ago about the Google Reader Notifier application for Windows computers and was linked by the Download Squad Website who mentioned the Firefox extension with the same name. The only difference between those two applications that share the same name is that one is running in your system tray while the other is reporting the amount of unread news in Google Reader in your status bar.
As usual you have to supply your login details to be able to check the unread items in your Google Reader account. Several other configuration options can be changed such as the refresh time in second which is set to 120 minutes by default and how the extension handles clicks on the icons.
If you move the mouse over the unread count all categories that contain unread items are displayed with the amount of unread items next to them. This is great if you only want to read feeds from a certain category for instance.
Read More:
Google Reader Notifier Download
via Download Squad
Related Articles:
Google Reader NotifierGmail, Google Reader, Wave And Voice Notifier For Google Chrome
Google Reader Essentials Userscript
Google Reader integrates with Google Talk
Google Reader Minimalistic Style