Gmail gets unread badge and desktop notifications for Chrome
There are numerous ways to display an unread messages badge for your Gmail account on a computer. Personally, I use a Fluid app (based on Safari) and the launch icon in my Mac’s dock features an unread messages badge. Chrome already shows unread message count in the page title for a tab, but if you pin your tabs or have a lot of them open, this count can be hidden. And how often do you miss a change in that number anyway? Many of you probably have your own workarounds or third-party hacks, but Google has finally released official solutions for Chrome users: an unread count badge on Chrome Gmail tabs and HTML5 desktop notifications for chat and messages.
The notifications can be enabled under “Settings > Desktop Notifications.” Chat and message notifications can be individually activated and deactivated. The unread message badge can be enabled under “Settings > Labs,” then search for “unread.”
Google is working on bringing the desktop notifications to browsers other than Chrome.
Via The Gmail Blog, 2

Might be the same thing but this also works in firefox. "Unread message icon by Manu C See how many unread messages are in your inbox with a quick glance at the tab's icon. This lab only works with Chrome (version 6 and above) and Firefox (version 2 and above)."
- spam
- offensive
- disagree
- off topic
Like