If we had to guess, we'd say that Gmail's latest Labs feature, putting an unread message count first in the title bar and tabs, was probably inspired by a certain Firefox add-on ...
... but who are we to divine what craziness lurks in the minds of Google's Gmail engineers? In any case, Gmail's Labs section now has a "Title Tweaks" option you can enable to put a count of unread messages in parentheses near the front of your Gmail page title, making it visible in most browser tabs and at the top of stand-alone windows. It's pretty much an official implementation of Gmail Inbox Display Unread Count FIRST, a Greasemonkey script written by our founding editor and Jon Ramsey, which was rolled into our all-in-one Better Gmail 2 Firefox extension.
Gmail's official version, however, shows the full message number, and keeps the icon the same colour. Want a 10-message limit to manage your inbox guilt, along with coloured icons? Try the previously mentioned Gmail FavIcon Alerts script.
Note to Offline Gmail users: Your Labs changes, including Title Tweaks, may take a few minutes to take effect and, in this editor's experience, cause browser instability. Save what you're doing before enabling.