Firefox 4: Most websites will add a number to the tab name if you have notifications to read, but they aren't exactly eye-catching. Extension Tab Badge makes sure you see which tabs are calling for your attention with a red badge.
Gmail may have added its own badge to Gmail Labs, but most sites don't draw your attention to their tabs that well. Tab Badge performs one simple task: it adds a red badge to tabs that are getting notifications. This is especially nice in situations where that number in parentheses would be hidden, like on pinned tabs or if you have a lot of tabs open. The badge will always show up on the tab, no matter how bit or small it is.
We'd love to see a feature that blacklists certain sites — I certainly don't need a big red "1000+" on my Google Reader tab at all times — but it is nice to have if you don't have some other external source sending you notifications.
Tab Badge is a free download, works wherever Firefox does. Note that you need to be running the Firefox 4 betas to use this extension (though if you aren't, we highly recommend you do — they're quite a step up).