Enables desktop notifications like in Chrome (e.g. Gmail, imo.im) and, if the site doesn’t support them, it can notify new messages or updates detecting changes of the title (e.g. Hotmail, Yahoo, Facebook, Twitter). Even if the browser is minimized!
Here is a little more about the add-on from the developers:
The extension can also show a desktop notification when the title of a tab changes while the tab is not focused. A desktop notification it’s an alert that appears outside the browser window, in a corner of your screen. Click on it to open the tab that triggered it. Besides chat, email and social networks, it works with tons of other websites, like microblogging sites and similar (e.g.: Twitter and Digg), or to show the title of a track when it starts to be played (e.g.: MySpace).
Want to learn more about this amazing add-on? You can pick up the Tab Notifier at the Firefox Add-ons website.