Firefox 4- Brings app tabs to you!
Firefox has a new tab menu entry, if you havent seen it already. it can be pretty sweet addition if you are a gmail user. Its called pin as app tab.
Goto labs in gmail and enable the Unread message icon extension. This shows a number in the tab icon indicating the number of inbox messages. Now make the thing an app tab – and viola. – Gmail Notifier right inside the firefox (which probably takes up most of your online life).